Light-Emitting Element, Light-Emitting Device, and Electronic Appliance

ABSTRACT

An object of the present invention is to provide a light-emitting element with high luminous efficiency, and a light-emitting element of low-voltage driving. Another object of the present invention is to provide a light-emitting device with low power consumption by using the light-emitting element. Another object of the present invention is to provide an electronic appliance with low power consumption by using the light-emitting device in a display portion. A light-emitting element includes, between a pair of electrodes, a layer containing a composite material of a first organic compound and an inorganic compound and a layer containing a second organic compound being in contact with the layer containing the composite material, wherein the second organic compound does not have a peak of an absorption spectrum in a wavelength region of 450 to 800 nm if the second organic compound is compounded with the inorganic compound.

TECHNICAL FIELD

The present invention relates to a light-emitting element of a currentexcitation type. Moreover, the present invention relates to alight-emitting device and an electronic appliance which have thelight-emitting elements.

BACKGROUND ART

In recent years, research and development have been extensively carriedout on a light-emitting element which uses an organic compound having alight-emitting property. In a basic structure of such a light-emittingelement, a layer which contains an organic compound having alight-emitting property is sandwiched between a pair of electrodes. Byapplying voltage to this element, electrons and holes are injected fromthe pair of electrodes respectively into the layer containing an organiccompound having a light-emitting property; thus, current flows. Then, byrecombination of those carries (electrons and holes), the organiccompound having a light-emitting property forms an excited state andemits light when the excited state returns to a ground state. Because ofsuch a mechanism, this light-emitting element is called a light-emittingelement of a current excitation type.

The excited state of the organic compound includes a singlet-excitedstate and a triplet-excited state, and light emission from asinglet-excited state is called fluorescence and light emission from atriplet-excited state is called phosphorescence. Such a light-emittingelement can be manufactured generally by using an organic thin film witha thickness of about 0.1 μm; therefore, the light-emitting element hasadvantages of thinness and lightness in weight. Moreover, since it takesabout 1 μs or shorter from carrier injection until light emission, veryhigh-speed response is also one of its advantages. Because of theseadvantages, the light-emitting element is considered to be preferable asa flat-panel display element.

Since the light-emitting element is formed into a film shape, surfacelight emission can be easily obtained by forming a large-sized element.This is a feature which is difficult to be obtained in point lightsources typified by an incandescent lamp and an LED or line lightsources typified by a fluorescent lamp. Accordingly, the light-emittingelement is also effectively used as a surface light source applicable toillumination and the like.

In display devices to be incorporated into various informationprocessing appliances which have rapidly developed recently, there is ademand particularly for lower power consumption, and decrease in drivevoltage for light-emitting elements has been attempted in order tofulfill this demand.

For example, according to Reference 1 (Japanese Patent ApplicationLaid-Open No. 2005-123095), an effect of decreasing drive voltage isobtained by using a layer in which vanadium oxide and α-NPD areco-evaporated.

However, the layer in which vanadium oxide and α-NPD are co-evaporatedhas a peak of an absorption spectrum in 400 to 800 nm, which is avisible region. In particular, the layer has a high peak of absorptionin about 150 to 500 nm, which is a blue region. Therefore, light emittedfrom a light-emitting substance is absorbed in the layer in whichvanadium oxide and α-NPD are co-evaporated, which leads to a problem inthat external extraction efficiency of light emission is lowered.

DISCLOSURE OF INVENTION

In view of the above problem, it is an object of the present inventionto provide a light-emitting element having high luminous efficiency.Moreover, it is an object of the present invention to provide alight-emitting element with low drive voltage. In addition, it is anobject of the present invention to provide a light-emitting device withlow power consumption by manufacturing the light-emitting device usingthe light-emitting element. Furthermore, it is an object of the presentinvention to provide an electronic appliance with low power consumptionby using the light-emitting device in a display portion.

As a result of concerted study, the present inventors have found thatthe objects can be achieved by applying a composite material of anorganic compound and an inorganic compound.

A light-emitting element according to the present invention includes alayer containing a composite material of a first organic compound and aninorganic compound; and a layer containing a second organic compound,which is provided so as to be in contact with the layer containing thecomposite material, wherein the layer containing the composite materialand the layer containing the second organic compound are providedbetween a pair of electrodes, and wherein the second organic compounddoes not have a peak of an absorption spectrum in a wavelength region of450 to 800 nm if the second organic compound is compounded with aninorganic compound.

A light-emitting element according to the present invention includes alayer containing a composite material of a first organic compound and aninorganic compound; a layer containing a second organic compound, whichis provided so as to be in contact with the layer containing thecomposite material; and a light-emitting layer containing alight-emitting substance, wherein the layer containing the compositematerial, the layer containing the second organic compound, and thelight-emitting layer are provided between a first electrode and a secondelectrode, wherein the second organic compound does not have a peak ofan absorption spectrum in a wavelength region of 450 to 800 nm if thesecond organic compound is compounded with the inorganic compound, andwherein the light-emitting substance emits light when voltage is appliedso that the first electrode has a higher potential than the secondelectrode.

A light-emitting element according to the present invention includes alayer containing a composite material of a first organic compound and aninorganic compound; a layer containing a second organic compound, whichis provided so as to be in contact with the layer containing thecomposite material; and a light-emitting layer containing alight-emitting substance, wherein the layer containing the compositematerial, the layer containing the second organic compound, and thelight-emitting layer are provided between a first electrode and a secondelectrode, wherein the layer containing the composite material isprovided so as to be in contact with the first electrode, wherein thesecond organic compound does not have a peak of an absorption spectrumin a wavelength region of 450 to 800 nm if the second organic compoundis compounded with the inorganic compound, and wherein thelight-emitting substance emits light when voltage is applied so that thefirst electrode has a higher potential than the second electrode.

A light-emitting element according to the present invention includes amultilayer body in which a layer containing a composite material of afirst organic compound and an inorganic compound and a layer containinga second organic compound, which is provided so as to be in contact withthe layer containing the composite material are stacked, wherein themultilayer body is provided between a pair of electrodes, and whereinthe multilayer body does not have a peak of an absorption spectrum in awavelength region of 450 to 800 nm.

A light-emitting element according to the present invention includes amultilayer body in which a layer containing a composite material of afirst organic compound and an inorganic compound and a layer containinga second organic compound, which is provided so as to be in contact withthe layer containing the composite material are stacked, wherein themultilayer body is provided between a pair of electrodes, wherein thecomposite material has a transmittance of 80% or higher in a wavelengthregion of 450 to 800 nm when the composite material has a thickness of100 nm, and wherein a composite material of the second organic compoundand the inorganic compound has a transmittance of 80% or higher in awavelength region of 450 to 800 nm when the composite material of thesecond organic compound and the inorganic compound has a thickness of100 nm.

A light-emitting element according to the present invention includes amultilayer body in which a layer containing a composite material of afirst organic compound and an inorganic compound and a layer containinga second organic compound, which is provided so as to be in contact withthe layer containing the composite material are stacked, wherein themultilayer body is provided between a pair of electrodes, wherein thecomposite material has an absorbance that satisfies the formula (1) in awavelength region of 450 to 800 nm, and wherein a composite material ofthe second organic compound and the inorganic compound has an absorbancethat satisfies the formula (1) in a wavelength region of 450 to 800 nm.

A≦9.7×10⁻⁴ ×l  (1)

-   -   A: absorbance    -   l: thickness (nm)

A light-emitting element according to the present invention includes alayer containing a composite material of a first organic compound and aninorganic compound; a layer containing a second organic compound, whichis provided so as to be in contact with the layer containing thecomposite material; and a light-emitting layer containing alight-emitting substance, wherein the layer containing the compositematerial, the layer containing the second organic compound, and thelight-emitting layer are provided between a first electrode and a secondelectrode, wherein a multilayer body in which the layer containing thecomposite material and the layer containing the second organic compoundare stacked does not have a peak of an absorption spectrum in awavelength region of 450 to 800 nm, and wherein the light-emittingsubstance emits light when voltage is applied so that the firstelectrode has a higher potential than the second electrode.

A light-emitting element according to the present invention includes alayer containing a composite material of a first organic compound and aninorganic compound; a layer containing a second organic compound, whichis provided so as to be in contact with the layer containing thecomposite material; and a light-emitting layer containing alight-emitting substance; wherein the layer containing the compositematerial, the layer containing the second organic compound, and thelight-emitting layer are provided between a first electrode and a secondelectrode, wherein the composite material has a transmittance of 80% orhigher in a wavelength region of 450 to 800 nm when the compositematerial has a thickness of 100 nm, wherein a composite material of thesecond organic compound and the inorganic compound has a transmittanceof 80% or higher in a wavelength region of 450 to 800 nm when thecomposite material of the second organic compound and the inorganiccompound has a thickness of 100 nm, and wherein the light-emittingsubstance emits light when voltage is applied so that the firstelectrode has a higher potential than the second electrode.

A light-emitting element according to the present invention includes alayer containing a composite material of a first organic compound and aninorganic compound; a layer containing a second organic compound, whichis provided so as to be in contact with the layer containing thecomposite material; and a light-emitting layer containing alight-emitting substance; wherein the layer containing the compositematerial, the layer containing the second organic compound, and thelight-emitting layer are provided between a first electrode and a secondelectrode, wherein the layer containing the composite material isprovided so as to be in contact with the first electrode, wherein amultilayer body in which the layer containing the composite material andthe layer containing the second organic compound are stacked does nothave a peak of an absorption spectrum in a wavelength region of 450 to800 nm, and wherein the light-emitting substance emits light whenvoltage is applied so that the first electrode has a higher potentialthan the second electrode.

A light-emitting element according to the present invention includes alayer containing a composite material of a first organic compound and aninorganic compound; a layer containing a second organic compound, whichis provided so as to be in contact with the layer containing thecomposite material; and a light-emitting layer containing alight-emitting substance; wherein the layer containing the compositematerial, the layer containing the second organic compound, and thelight-emitting layer are provided between a first electrode and a secondelectrode, wherein the layer containing the composite material isprovided so as to be in contact with the first electrode, wherein thecomposite material has a transmittance of 80% or higher in a wavelengthregion of 450 to 800 nm when the composite material has a thickness of100 nm, wherein a composite material of the second organic compound andthe inorganic compound has a transmittance of 80% or higher in awavelength region of 450 to 800 nm when the composite material of thesecond organic compound and the inorganic compound has a thickness of100 nm, and wherein the light-emitting substance emits light whenvoltage is applied so that the first electrode has a higher potentialthan the second electrode.

A light-emitting element according to the present invention includes alayer containing a composite material of a first organic compound and aninorganic compound; a layer containing a second organic compound, whichis provided so as to be in contact with the layer containing thecomposite material; and a light-emitting layer containing alight-emitting substance, wherein the layer containing the compositematerial, the layer containing the second organic compound, and thelight-emitting layer are provided between a first electrode and a secondelectrode, wherein the layer containing the composite material isprovided so as to be in contact with the first electrode, wherein thecomposite material has an absorbance that satisfies the formula (1) in awavelength region of 450 to 800 nm, wherein a composite material of thesecond organic compound and the inorganic compound has an absorbancethat satisfies the formula (1) in a wavelength region of 450 to 800 nm,and wherein the light-emitting substance emits light when voltage isapplied so that the first electrode has a higher potential than thesecond electrode.

A≦9.7×10⁴ ×l  (1)

-   -   A: absorbance    -   l: thickness (nm)

In the above structure, the first organic compound is preferablyaromatic hydrocarbon. In particular, the first organic compound ispreferably an anthracene derivative.

A light-emitting element according to the present invention includes amultilayer body in which a layer containing a composite material of afirst organic compound and an inorganic compound and a layer containinga second organic compound, which is provided so as to be in contact withthe layer containing the composite material are stacked, wherein themultilayer body is provided between a pair of electrodes, and whereinthe first organic compound is aromatic hydrocarbon.

A light-emitting element according to the present invention includes amultilayer body in which a layer containing a composite material of afirst organic compound and an inorganic compound and a layer containinga second organic compound, which is provided so as to be in contact withthe layer containing the composite material are stacked, wherein themultilayer body is provided between a pair of electrodes, and whereinthe first organic compound is an anthracene derivative.

In the above structure, the second organic compound preferably has ahigher ionization potential than the first organic compound by 0.5 eV orlower, more preferably 0.3 eV or lower, and much more preferably 0.1 eVor lower. In other words, the following formula is preferably satisfiedwhere Ip (1) is the ionization potential of the first organic compoundand Ip (2) is the ionization potential of the second organic compound.

Ip(2)≦Ip(1)+0.5 eV

It is more preferable that the following formula be satisfied.

Ip(2)≦Ip(1)+0.3 eV

It is much more preferable that the following formula be satisfied.

Ip(2)≦Ip(1)+0.1 eV

In the above structure, the second organic compound is preferablyaromatic hydrocarbon or a carbazole derivative. In particular, thesecond organic compound is preferably an anthracene derivative.

In the above structure, the layer containing the second organic compoundpreferably has a thickness of 1 to 20 nm.

In the above structure, the inorganic compound preferably has anelectron-accepting property with respect to the first organic compound.

Moreover, the inorganic compound is preferably an oxide of a transitionmetal. In particular, the inorganic compound is preferably an oxide of ametal belonging to any of Group 4 to Group 8 in the periodic table. Itis more preferable that the inorganic compound be any of vanadium oxide,niobium oxide, tantalum oxide, chromium oxide, molybdenum oxide,tungsten oxide, manganese oxide, and rhenium oxide.

A light-emitting element according to the present invention includes alayer containing a composite material of an organic compound and aninorganic compound; and a layer containing the organic compound, whichis provided so as to be in contact with the layer containing thecomposite material, wherein the layer containing the composite materialand the layer containing the organic compound are provided between apair of electrodes, and wherein the composite material does not have apeak of an absorption spectrum in a wavelength region of 450 to 800 nm.

A light-emitting element according to the present invention includes alayer containing a composite material of an organic compound and aninorganic compound; and a layer containing the organic compound, whichis provided so as to be in contact with the layer containing thecomposite material, wherein the layer containing the composite materialand the layer containing the organic compound are provided between apair of electrodes, and wherein the composite material has atransmittance of 80% or higher in a wavelength region of 450 to 800 nmwhen the composite material has a thickness of 100 nm.

A light-emitting element according to the present invention includes alayer containing a composite material of an organic compound and aninorganic compound; and a layer containing the organic compound, whichis provided so as to be in contact with the layer containing thecomposite material, wherein the layer containing the composite materialand the layer containing the organic compound are provided between apair of electrodes, and wherein the composite material has an absorbancethat satisfies the formula (1) in a wavelength region of 450 to 800 nm.

A≦9.7×10⁻⁴ ×l  (1)

-   -   A: absorbance    -   l: thickness (nm)

A light-emitting element according to the present invention includes alayer containing a composite material of an organic compound and aninorganic compound; a layer containing the organic compound, which isprovided so as to be in contact with the layer containing the compositematerial; and a light-emitting layer containing a light-emittingsubstance; wherein the layer containing the composite material, thelayer containing the organic compound, and the light-emitting layer areprovided between a first electrode and a second electrode, wherein thecomposite material does not have a peak of an absorption spectrum in awavelength region of 450 to 800 nm, and wherein the light-emittingsubstance emits light when voltage is applied so that the firstelectrode has a higher potential than the second electrode.

A light-emitting element according to the present invention includes alayer containing a composite material of an organic compound and aninorganic compound; a layer containing the organic compound, which isprovided so as to be in contact with the layer containing the compositematerial; and a light-emitting layer containing a light-emittingsubstance; wherein the layer containing the composite material, thelayer containing the organic compound, and the light-emitting layer areprovided between a first electrode and a second electrode, wherein thecomposite material has a transmittance of 80% or higher in a wavelengthregion of 450 to 800 nm when the composite material has a thickness of100 nm, and wherein the light-emitting substance emits light whenvoltage is applied so that the first electrode has a higher potentialthan the second electrode.

A light-emitting element according to the present invention includes alayer containing a composite material of an organic compound and aninorganic compound; a layer containing the organic compound, which isprovided so as to be in contact with the layer containing the compositematerial; and a light-emitting layer containing a light-emittingsubstance; wherein the layer containing the composite material, thelayer containing the organic compound, and the light-emitting layer areprovided between a first electrode and a second electrode, wherein thecomposite material does not have a peak of an absorption spectrum in awavelength region of 450 to 800 nm, and wherein the light-emittingsubstance emits light when voltage is applied so that the firstelectrode has a higher potential than the second electrode.

A light-emitting element according to the present invention includes alayer containing a composite material of an organic compound and aninorganic compound; a layer containing the organic compound, which isprovided so as to be in contact with the layer containing the compositematerial; and a light-emitting layer containing a light-emittingsubstance, wherein the layer containing the composite material, thelayer containing the organic compound, and the light-emitting layer areprovided between a first electrode and a second electrode, wherein thelayer containing the composite material is provided so as to be incontact with the first electrode, wherein the composite material has atransmittance of 80% or higher in a wavelength region of 450 to 800 nmwhen the composite material has a thickness of 100 nm, and wherein thelight-emitting substance emits light when voltage is applied so that thefirst electrode has a higher potential than the second electrode.

A light-emitting element according to the present invention includes alayer containing a composite material of an organic compound and aninorganic compound; a layer containing the organic compound, which isprovided so as to be in contact with the layer containing the compositematerial; and a light-emitting layer containing a light-emittingsubstance, wherein the layer containing the composite material, thelayer containing the organic compound, and the light-emitting layer areprovided between a first electrode and a second electrode, wherein thelayer containing the composite material is provided so as to be incontact with the first electrode, wherein the composite material has anabsorbance that satisfies the formula (1) in a wavelength region of 450to 800 nm, and wherein the light-emitting substance emits light whenvoltage is applied so that the first electrode has a higher potentialthan the second electrode.

A≦9.7×10⁻⁴ ×l  (1)

-   -   A: absorbance    -   l: thickness (nm)

In the above structure, the organic compound is preferably aromatichydrocarbon. In particular, the organic compound is preferably ananthracene derivative.

A light-emitting element according to the present invention includes alayer containing a composite material of an organic compound and aninorganic compound; and a layer containing the organic compound, whichis provided so as to be in contact with the layer containing thecomposite material, wherein the layer containing the composite materialand the layer containing the organic compound are provided between apair of electrodes, and wherein the organic compound is aromatichydrocarbon.

A light-emitting element according to the present invention includes alayer containing a composite material of an organic compound and aninorganic compound; and a layer containing the organic compound, whichis provided so as to be in contact with the layer containing thecomposite material, wherein the layer containing the composite materialand the layer containing the organic compound are provided between apair of electrodes, and wherein the organic compound is an anthracenederivative.

In the above structure, the layer containing the organic compoundpreferably has a thickness of 1 to 20 nm.

In the above structure, the inorganic compound preferably has anelectron-accepting property with respect to the first organic compound.

Moreover, the inorganic compound is preferably an oxide of a transitionmetal. In particular, the inorganic compound is preferably an oxide of ametal belonging to any of Group 4 to Group 8 in the periodic table. Itis more preferable that the inorganic compound be any of vanadium oxide,niobium oxide, tantalum oxide, chromium oxide, molybdenum oxide,tungsten oxide, manganese oxide, and rhenium oxide.

It is to be noted that the present invention includes in its category alight-emitting device having any of the aforementioned light-emittingelements. The light-emitting device in this specification includes animage display device, a light-emitting device, and a light source(including an illumination device). Further, the light-emitting deviceincludes a module in which a connector such as an FPC (Flexible PrintedCircuit), a TAB (Tape Automated Bonding) tape, or a TCP (Tape CarrierPackage) is attached to a panel where the light-emitting element isformed, a module in which a print wiring board is provided at an end ofa TAB tape or an TCP, and a module in which an IC (Integrated Circuit)is directly mounted on the light-emitting element by a COG (Chip OnGlass) method.

An electronic appliance using the light-emitting element of the presentinvention in its display portion is also included in the category of thepresent invention. Therefore, the electronic appliance of the presentinvention is equipped with the aforementioned light-emitting element anda controller for controlling light emission of the light-emittingelement in its display portion.

By applying the present invention, a light-emitting element having highluminous efficiency can be obtained.

Moreover, by applying the present invention, a light-emitting elementdriven at low voltage can be obtained.

By applying the present invention, a light-emitting device with lowpower consumption can be obtained.

By applying the present invention, an electronic appliance with lowpower consumption can be obtained.

BRIEF DESCRIPTION OF DRAWINGS

In the accompanying drawings:

FIGS. 1A to 1C describe light-emitting elements of the presentinvention;

FIG. 2 describes a light-emitting element of the present invention;

FIG. 3 describes a light-emitting element of the present invention;

FIG. 4 shows transmittance of a composite material;

FIG. 5 shows transmittance of a composite material;

FIG. 6 shows a current-voltage characteristic of a light-emittingelement;

FIG. 7 shows a luminance-voltage characteristic of a light-emittingelement;

FIG. 8 shows a current efficiency-luminance characteristic of alight-emitting element;

FIG. 9 shows a current-voltage characteristic of a light-emittingelement;

FIG. 10 shows a luminance-voltage characteristic of a light-emittingelement;

FIG. 11 shows a current efficiency-luminance characteristic of alight-emitting element;

FIG. 12 shows a current-voltage characteristic of a light-emittingelement;

FIG. 13 shows a luminance-voltage characteristic of a light-emittingelement;

FIG. 14 shows a current efficiency-luminance characteristic of alight-emitting element;

FIG. 15 shows a current-voltage characteristic of a light-emittingelement;

FIG. 16 shows a luminance-voltage characteristic of a light-emittingelement;

FIG. 17 shows a current efficiency-luminance characteristic of alight-emitting element;

FIG. 18 shows a current-voltage characteristic of a light-emittingelement;

FIG. 19 shows a luminance-voltage characteristic of a light-emittingelement;

FIG. 20 shows a current efficiency-luminance characteristic of alight-emitting element;

FIG. 21 shows a current-voltage characteristic of a light-emittingelement;

FIG. 22 shows a luminance-voltage characteristic of a light-emittingelement;

FIG. 23 shows a current efficiency-luminance characteristic of alight-emitting element;

FIG. 24 shows a current-voltage characteristic of a light-emittingelement;

FIG. 25 shows a luminance-voltage characteristic of a light-emittingelement;

FIG. 26 shows a current efficiency-luminance characteristic of alight-emitting element;

FIG. 27 shows a current-voltage characteristic of a light-emittingelement;

FIG. 28 shows a luminance-voltage characteristic of a light-emittingelement;

FIG. 29 shows a current efficiency-luminance characteristic of alight-emitting element;

FIG. 30 shows a current-voltage characteristic of a light-emittingelement;

FIG. 31 shows a luminance-voltage characteristic of a light-emittingelement;

FIG. 32 shows a current efficiency-luminance characteristic of alight-emitting element;

FIGS. 33A and 33B describe a light-emitting device of the presentinvention;

FIG. 34 describes a light-emitting device of the present invention;

FIGS. 35A to 35D describe electronic appliances of the presentinvention;

FIG. 36 describes an electronic appliance of the present invention;

FIG. 37 shows an absorption spectrum of a composite material;

FIG. 38 shows an absorption spectrum of a composite material;

FIG. 39 shows a current-voltage characteristic of a light-emittingelement;

FIG. 40 shows a luminance-voltage characteristic of a light-emittingelement; and

FIG. 41 shows a current efficiency-luminance characteristic of alight-emitting element.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment modes and embodiments of the present invention will behereinafter described with reference to the accompanying drawings.However, the present invention is not restricted to the followingdescription and it is easily understood by those skilled in the art thatthe mode and detail can be variously changed without departing from thescope and spirit of the present invention. Therefore, the presentinvention is not construed as being restricted to the description of theembodiment modes and embodiments hereinafter shown.

Embodiment Mode 1

This embodiment mode will describe a composite material which is usedfor a light-emitting element of the present invention. In thisspecification, being composite means not only a simple mixture of twomaterials but also a change into such a state that charges aretransported between two materials through a mixture of the materials ata molecular level.

The composite material used in the present invention is a compositematerial of a first organic compound and an inorganic compound. As thefirst organic compound for the composite material, various compoundssuch as an aromatic amine compound, a carbazole derivative, aromatichydrocarbon, and a high-molecular compound (such as oligomer, dendrimer,or polymer) can be used. The first organic compound used for thecomposite material is preferably an organic compound having a highhole-transporting property. Specifically, a substance having a holemobility of 10⁻⁶ cm²/Vs or higher is preferably used. However, othersubstances than those may also be used as long as the substances havehigher hole-transporting properties than electron-transportingproperties. The first organic compound which can be used for thecomposite material is specifically shown below.

For example, the followings can be given as the aromatic amine compound:N,N′-di(p-tolyl)-N,N′-diphenyl-p-phenylenediamine (abbreviation:DTDPPA); 4,4′-bis[N-(4-diphenylaminophenyl)-N-phenylamino]biphenyl(abbreviation: DPAB);4,4′-bis(N-{4-[N-(3-methylphenyl)-N-phenylamino]phenyl}-N-phenylamino)biphenyl(abbreviation: DNTPD);1,3,5-tris[N-(4-diphenylaminophenyl)-N-phenylamino]benzene(abbreviation: DPA3B); and the like.

As the carbazole derivative which can be used for the compositematerial, the followings can be given specifically:3-[N-9-phenylcarbazole-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzPCA1);3,6-bis[N-(9-phenylcarbazole-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzPCA2);3-[N-(1-naphtyl)-N-(9-phenylcarbazole-3-yl)amino]-9-phenylcarbazole(abbreviation: PCzPCN1); and the like.

Moreover, 4,4′-di(N-carbazolyl)biphenyl (abbreviation: CBP);1,3,5-tris[4-(N-carbazolyl)phenyl]benzene (abbreviation: TCPB);9-[4-(N-carbazolyl)]phenyl-10-phenylanthracene (abbreviation: CZPA);2,3,5,6-triphenyl-1,4-bis[4-(N-carbazolyl)phenyl]benzene; or the likecan also be used.

As the aromatic hydrocarbon which can be used for the compositematerial, the followings can be given for example: an anthracenederivative such as 9,10-di(naphthalene-2-yl)-2-tert-butylanthracene(abbreviation: t-BuDNA);9,10-di(naphthalene-1-yl)-2-tert-butylanthracene;9,10-bis(3,5-diphenylphenyl)anthracene (abbreviation: DPPA);9,10-di(4-phenylphenyl)-2-tert-butylanthracene (abbreviation: t-BuDBA);9,10-di(naphthalene-2-yl)anthracene (abbreviation: DNA);9,10-diphenylanthracene (abbreviation: DPAnth); 2-tert-butylanthracene(abbreviation: t-BuAnth); 9,10-di(4-methylnaphthalene-1-yl)anthracene(abbreviation: DMNA);2-tert-butyl-9,10-bis[2-(naphthalene-1-yl)phenyl]anthracene;

-   9,10-bis[2-(naphthalene-1-yl)phenyl]anthracene;-   2,3,6,7-tetramethyl-9,10-di(naphthalene-1-yl)anthracene;-   2,3,6,7-tetramethyl-9,10-di(naphthalene-2-yl)anthracene;    9,9′-bianthryl; 10,10′-diphenyl-9,9′-bianthryl;    10,10′-di(2-phenylphenyl)-9,9′-bianthryl;    10,10′-bis[(2,3,4,5,6-pentaphenyl)phenyl]-9,9′-bianthryl;    anthracene, and the like; tetracene; rubrene; perylene;    2,5,8,11-tetra(tert-butyl)perylene; and the like. Beside those,    pentacene, coronene, or the like can also be used. In this way, the    aromatic hydrocarbon which has a hole mobility of 1×10⁻⁶ cm²/Vs or    higher and which has 14 to 42 carbon atoms is particularly    preferable.

The aromatic hydrocarbon which can be used for the composite materialmay have a vinyl skeleton. As the aromatic hydrocarbon having a vinylgroup, the followings are given for example:4,4′-bis(2,2-diphenylvinyl)biphenyl (abbreviation: DPVBi);9,10-bis[4-(2,2-diphenylvinyl)phenyl]anthracene (abbreviation: DPVPA);and the like.

Moreover, a high molecular compound such as poly(N-vinylcarbazole)(abbreviation: PVK) or poly(4-vinyltriphenylamine) (abbreviation: PVTPA)can also be used.

As the inorganic compound used for the composite material, an oxide of atransition metal is preferable. Moreover, an oxide of a metal belongingto any of Group 4 to Group 8 in the periodic table is preferable.Specifically, vanadium oxide, niobium oxide, tantalum oxide, chromiumoxide, molybdenum oxide, tungsten oxide, manganese oxide, and rheniumoxide are preferable because of their high electron-acceptingproperties. Above all, molybdenum oxide is particularly preferablebecause it is stable in the air, easily treated, and has a lowmoisture-absorption property.

A method for manufacturing a layer containing the composite material maybe either a wet method or a dry method, and any method may be used. Forexample, the layer containing the composite material can be manufacturedby co-evaporating the aforementioned organic compound and inorganiccompound. Moreover, the layer containing the composite material can alsobe obtained in such a way that a solution containing the aforementionedorganic compound and a metal alkoxide is applied and baked. Sincemolybdenum oxide is easily evaporated in vacuum, molybdenum oxide isalso preferable from the aspect of a manufacturing process.

The composite material used in the present invention does not have anabsorption peak in a wavelength region of 450 to 800 nm. Moreover, thecomposite material has a transmittance of 80% or higher in a wavelengthregion of 450 to 800 nm when the film thickness is 100 nm. Therefore,light emission from a light-emitting region can be effectively extractedto the outside.

Embodiment Mode 2

This embodiment mode will describe a layer containing a second organiccompound, which is provided so as to be in contact with the compositematerial of the first organic compound and the inorganic compound shownin Embodiment Mode 1.

The second organic compound in the layer containing the second organiccompound, which is provided so as to be in contact with the layercontaining the composite material, does not have an absorption peak in awavelength region of 450 to 800 nm, in the case where the second organiccompound is compounded with the inorganic compound in the compositematerial. A composite material containing the second organic compoundand the inorganic compound with the same mixture ratio as the firstorganic compound and the inorganic compound of the layer containing thecomposite material has a transmittance of 80% or higher in a wavelengthregion of 450 to 800 nm when the film thickness is 100 nm.

As the second organic compound, various compounds such as an aromaticamine compound, a carbazole derivative, aromatic hydrocarbon, and a highmolecular compound (such as oligomer, dendrimer, or polymer) can beused. As the second organic compound, an organic compound having a highhole-transporting property is preferable. Specifically, a substancehaving a hole mobility of 10⁻⁶ cm²/Vs or higher is preferable. However,other substances than those may also be used as long as the substanceshave higher hole-transporting properties than electron-transportingproperties. The second organic compound is hereinafter shownspecifically.

For example, the followings can be given as the aromatic amine compound:N,N-di(p-tolyl)-N,N′-diphenyl-p-phenylenediamine (abbreviation: DTDPPA);4,4′-bis[N-(4-diphenylaminophenyl)-N-phenylamino]biphenyl (abbreviation:DPAB);4,4′-bis(N-{4-[N-(3-methylphenyl)-N-phenylamino]phenyl}-N-phenylamino)biphenyl(abbreviation: DNTPD);1,3,5-tris[N-(4-diphenylaminophenyl)-N-phenylamino]benzene(abbreviation: DPA3B); and the like.

As the carbazole derivative, the followings can be given specifically:3-[N-(9-phenylcarbazole-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCZPCA1);3,6-bis[N-(9-phenylcarbazole-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzPCA2);3-[N-(1-naphtyl)-N-(9-phenylcarbazole-3-yl)amino]-9-phenylcarbazole(abbreviation: PCzPCN1); and the like.

Moreover, 4,4′-di(N-carbazolyl)biphenyl (abbreviation. CBP);1,3,5-tris[4-(N-carbazolyl)phenyl]benzene (abbreviation: TCPB);9-[4-(N-carbazolyl)]phenyl-10-phenylanthracene (abbreviation: CZPA);2,3,5,6-triphenyl-1,4-bis[4-(N-carbazolyl)phenyl]benzene; or the likecan also be used.

As the aromatic hydrocarbon, the followings can be given for example: ananthracene derivative such as9,10-di(naphthalene-2-yl)-2-tert-butylanthracene (abbreviation:t-BuDNA); 9,10-di(naphthalene-1-yl)-2-tert-butylanthracene;9,10-bis(3,5-diphenylphenyl)anthracene (abbreviation: DPPA);9,10-di(4-phenylphenyl)-2-tert-butylanthracene (abbreviation: t-BuDBA);9,10-di(naphthalene-2-yl)anthracene (abbreviation: DNA);9,10-diphenylanthracene (abbreviation: DPAnth); 2-tert-butylanthracene(abbreviation: t-BuAnth); 9,10-di(4-methylnaphthalene-1-yl)anthracene(abbreviation: DMNA);2-tert-butyl-9,10-bis[2-(naphthalene-1-yl)phenyl]anthracene;9,10-bis[2-(naphthalene-1-yl)phenyl]anthracene;2,3,6,7-tetramethyl-9,10-di(naphthalene-1-yl)anthracene;2,3,6,7-tetramethyl-9,10-di(naphthalene-2-yl)anthracene; 9,9′-bianthryl;10,10′-diphenyl-9,9′-bianthryl;10,10′-di(2-phenylphenyl)-9,9′-bianthryl;10,10′-bis[(2,3,4,5,6-pentaphenyl)phenyl]-9,9′-bianthryl; anthracene;and the like, tetracene; rubrene; perylene;2,5,8,11-tetra(tert-butyl)perylene; and the like. Beside those,pentacene, coronene, or the like can also be used. In this way, aromatichydrocarbon which has a hole mobility of 1×10⁻⁶ cm²/Vs or higher andwhich has 14 to 42 carbon atoms is particularly preferable.

The aromatic hydrocarbon may have a vinyl skeleton. As the aromatichydrocarbon having a vinyl group, the followings are given for example:4,4′-bis(2,2-diphenylvinyl)biphenyl (abbreviation: DPVBi);9,10-bis[4-(2,2-diphenylvinyl)phenyl]anthracene (abbreviation: DPVPA);and the like.

Moreover, a high molecular compound such as poly(N-vinylcarbazole)(abbreviation: PVK) or poly(4-vinyltriphenylamine) (abbreviation: PVTPA)can also be used.

The layer containing the second organic compound does not have a peak ofan absorption spectrum in a wavelength region of 450 to 800 nm, if thesecond organic compound is compounded with the inorganic compoundcontained in the composite material. Moreover, if the second organiccompound is compounded with the inorganic compound with the same mixtureratio as the first organic compound and the inorganic compound in thelayer containing the composite material, the transmittance is 80% orhigher in a wavelength region of 450 to 800 nm when the film thicknessis 100 nm. Therefore, even if the second organic compound and theinorganic compound in the layer containing the composite material existas a composite material when the layer containing the composite materialand the layer containing the second organic compound are in contact witheach other and the inorganic compound in the layer containing thecomposite material and the second organic compound are in contact witheach other at an interface between the layer containing the compositematerial and the layer containing the second organic compound, lightemitted from the light-emitting substance is not absorbed and istransmitted through the composite material efficiently. Thus, externalextraction efficiency can be improved. In other words, a light-emittingelement having high luminous efficiency can be obtained.

Embodiment Mode 3

A light-emitting element of the present invention has a plurality oflayers between a pair of electrodes. The plurality of layers are stackedby combining layers which contain a substance having a highcarrier-injecting property and a substance having a highcarrier-transporting property so that a light-emitting region is formedapart from the electrodes, i.e., so that carries are recombined at aportion away from the electrodes.

A mode of a light-emitting element of the present invention will behereinafter described with reference to FIG. 1A.

In this embodiment mode, the light-emitting element includes a firstelectrode 102; a first layer 103, a second layer 104, a third layer 105,and a fourth layer 106 which are stacked sequentially over the firstelectrode 102; and a second electrode 107 provided over the fourth layer106. In this embodiment mode, the first electrode 102 functions as ananode and the second electrode 107 functions as a cathode.

The substrate 101 is used to support the light-emitting element. Thesubstrate 101 may be made of, for example, glass, plastic, or the like.Other materials than those may also be used as long as thelight-emitting element can be supported during a manufacturing process.

As the first electrode 102, various metals, alloys, conductivecompounds, or mixture thereof can be used. For example, indium tin oxide(ITO), indium tin oxide containing silicon, or indium zinc oxide (IZO)in which zinc oxide (ZnO) is mixed by 2 to 20 wt % into indium oxide canbe used. In addition, gold (Au), platinum (Pt), nickel (Ni), tungsten(W), chromium (Cr), molybdenum (Mo), iron (Fe), cobalt (Co), titanium(Ti), copper (Cu), palladium (Pd), aluminum (Al), aluminum-silicon(Al—Si), aluminum-titanium (Al—Ti), aluminum-silicon-copper (Al—Si—Cu),a nitride of a metal material (such as TiN), or the like can be used. Ifthe first electrode is used as an anode, it is preferable to use, amongthose materials, a material having a high work function (work functionof 4.0 eV or higher), or the like.

In a light-emitting element of the present invention, the firstelectrode 102 can be formed by using not only a material having a highwork function but also a material having a low work function.

The first layer 103 contains the composite material shown in EmbodimentMode 1. That is, the first layer 103 contains the composite material ofthe first organic compound and the inorganic compound.

The composite material in the first layer 103 does not have a peak of anabsorption spectrum in a wavelength region of 450 to 800 nm. Moreover,the composite material in the first layer 103 has a transmittance of 80%or higher over the entire wavelength region of 450 to 800 nm when thefirst layer has a film thickness of 100 nm. Therefore, light emittedfrom the light-emitting substance can be transmitted efficiently toimprove external extraction efficiency. That is, a light-emittingelement with high luminous efficiency can be obtained.

A method for manufacturing the layer containing the composite materialmay be either a wet method or a dry method, and any method may be used.For example, the layer containing the composite material can bemanufactured by co-evaporating the aforementioned organic compound andinorganic compound. Moreover, the layer containing the compositematerial can also be obtained in such a way that a solution containingthe aforementioned organic compound and metal alkoxide is applied andbaked. Since molybdenum oxide is easily evaporated in vacuum, molybdenumoxide is also preferable from the aspect of a manufacturing process.

The second layer 104 contains the second organic compound shown inEmbodiment Mode 2. In other words, the second layer 104 contains thesecond organic compound which does not have a peak of an absorptionspectrum in a wavelength region of 450 to 800 nm if the second organiccompound is compounded with the inorganic compound in the compositematerial contained in the first layer 103.

The second organic compound preferably has a higher ionization potentialthan the first organic compound in the first layer 103 by 0.5 eV orlower, more preferably 0.3 eV or lower, and much more preferably 0.1 eVor lower. In other words, the following formula is preferably satisfiedwhere Ip (1) is the ionization potential of the first organic compoundand Ip (2) is the ionization potential of the second organic compound.

Ip(2)≦Ip(1)+0.5 eV

It is more preferable that the following formula be satisfied.

Ip(2)≦Ip(1)+0.3 eV

It is much more preferable that the following formula be satisfied.

Ip(2)≦Ip(1)+0.1 eV

When the ionization potentials of the second organic compound and thefirst organic compound satisfy the above formulas, a carrier injectionbarrier between the first layer 103 and the second layer 104 is lowered;thus, drive voltage can be decreased. Therefore, if an organic compoundhaving a high ionization potential such as aromatic hydrocarbon is usedfor the first organic compound in the first layer 103, the range of theionization potential of the second organic compound which can be usedfor the second layer 104 can be widened, allowing the selection range ofthe second organic compound to be wider. For example, aromatichydrocarbon can be used for the first organic compound in the firstlayer 103 and the second organic compound in the second layer 104. Inthis way, a light-emitting element not including an amine compound canalso be manufactured.

Measured values of specific ionization potentials of compounds that canbe used as the first organic compound or the second organic compound areshown in Table 1.

TABLE 1 Value of ionization Compound potential (eV)9,10-bis(3,5-diphenylphenyl)anthracene (abbreviation: 5.83 DPPA)9,10-di(naphthalene-2-yl)anthracene (abbreviation: 5.81 DNA)9,10-di(naphthalene-2-yl)-2-tert-butylanthracene 5.55 (abbreviation:t-BuDNA) 9,10-di(naphthalene-1-yl)-2-tert-butylanthracene 5.789,10-diphenylanthracene (abbreviation: DPAnth) 5.749,10-bis[2-(naphthalene-1-yl)phenyl]anthracene 5.672,3,6,7-tetramethyl-9,10-di(naphthalene-1-yl)anthracene 5.702,3,6,7-tetramethyl-9,10-di(naphthalene-2-yl)anthracene 5.5410,10′-di(2-phenylphenyl)9,9′-bianthryl 5.81

In this specification, the ionizing potential is measured byphotoelectron spectroscopy in the air. For example, AC-2 manufactured byRIKEN KEIKI Co., Ltd. is used as a device for such measurement. Anobject to be measured was a thin film formed over a glass substrate byan evaporation method.

When aromatic hydrocarbon is used for the first organic compound in thefirst layer 103 and the second organic compound in the second layer 104,a light-emitting element having high heat resistance can bemanufactured. In general, when a bond of carbon and a hetero atom suchas oxygen, nitrogen, or sulfur exists in a molecule, flexibility of amolecular skeleton thereof improves; therefore a thermophysical propertysuch as glass transition temperature or a melting point is degraded.Accordingly, in a similar molecular structure, aromatic hydrocarbon hasa higher thermophysical property than an aromatic amine compound. Thus,a light-emitting element having high heat resistance can be obtained byusing aromatic hydrocarbon, as compared with the case of using anaromatic amine compound having a similar molecular structure.

In order that an amine compound may have high glass transitiontemperature and a high melting point, it is necessary to increase themolecular weight. Therefore, a starburst amine compound and a linearoligoamine compound have been synthesized so far; however, suchcompounds need a number of steps for being synthesized and it takes longtime and costs much to obtain a target material. Therefore, by usingaromatic hydrocarbon, cost required for obtaining a light-emittingelement having similar heat resistance can be reduced.

It is preferable that the organic compounds in the first layer 103 andthe second layer 104 be formed with the same substance, i.e., the firstorganic compound and the second organic compound be formed with the samesubstance, because a carrier injection barrier between the first layer103 and the second layer 104 becomes low. If the first layer 103 and thesecond layer 104 are formed by an evaporation method, they can be formedcontinuously; therefore, a manufacturing process can be simplified andthe productivity can be improved.

The film thickness of the second layer 104 preferably ranges from 1 to20 nm.

As shown in FIG. 3, a layer 108 which contains a substance having a highhole-transporting property may be provided between the second layer 104and the third layer 105. As the substance having a highhole-transporting property, for example, the following aromatic aminecompounds (I.e., compounds having a bond of a benzene ring and nitrogen)are given: 4,4′-bis[N-1-naphtyl)-N-phenylamino]biphenyl (abbreviation:NPB or α-NPD);N,N′-bis(3-methylphenyl)-N,N′-diphenyl-[1,1′-biphenyl]4,4′-diamine(abbreviation: TPD); 4,4′,4″-tris(N,N-diphenylamino)triphenylamine(abbreviation: TDATA);4,4′,4″-tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine(abbreviation; MTDATA); 4,4′-bis[N-phenyl-N-spirofluorene-2-yl)]biphenyl(abbreviation: BSPB); and the like. The substances mentioned here mainlyhave a hole mobility of 10⁻⁶ cm²/Vs or higher. However, other substancesthan those may be used as long as the substances have a higherhole-transporting property than an electron-transporting property.Moreover, the layer which contains a substance having a highhole-transporting property may be a single layer or may be formed bystacking two or more layers containing the above substances.

The third layer 105 contains a substance having a high light-emittingproperty. For example, a substance having a high light-emitting propertyand a substance having a high carrier-transporting property and havinghigh film quality (i.e., difficult to be crystallized) are freelycombined to form the third layer 105. The substance having a highlight-emitting property is N,N′-dimethylquinacridone (abbreviation:DMQd); N,N′-diphenylquinacridone (abbreviation: DPQd);3-(2-benzothiazoyl)-7-diethylaminocoumarin (abbreviation: coumarin 6);or the like. The substance having a high carrier-transporting propertyand having high film quality is tris(8-quinolinolato)aluminum(abbreviation: Alq); 9,10-di(2-naphtyl)anthracene (abbreviation: DNA);or the like. However, since Alq and DNA have high light-emittingproperties, the third layer 105 may be formed with any of thesesubstances alone.

The fourth layer 106 contains a substance having a highelectron-transporting property; for example, the following metal complexhaving a quinoline skeleton or a benzoquinoline skeleton, or the like isgiven: tris(8-quinolinolato)aluminum (abbreviation: Alq);tris(5-methyl-8-quinolinolato)aluminum (abbreviation: Almq₃);bis(10-hydroxybenzo[h]-quinolinato)beryllium (abbreviation: BeBq₂);bis(2-methyl-8-quinolinolato)-4-phenylphenolato-aluminum (abbreviation:BAlq); or the like. Beside those, a metal complex having an oxazoleligand or a thiazole ligand, such asbis[2-(2-hydroxyphenyl)-benzoxazolato]zinc (abbreviation: Zn(BOX)₂); orbis[2-(2-hydroxyphenyl)-benzothiazolato]zinc (abbreviation: Zn(BTZ)₂);or the like can also be used. In addition to the metal complex,2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviation:PBD); 1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene(abbreviation: OXD-7);3-(4-tert-butylphenyl)-4-phenyl-5-(4-biphenylyl)-1,2,4-triazole(abbreviation: TAZ);3-(4-tert-butylphenyl)-4-(4-ethylphenyl)-5-(4-biphenylyl)-1,2,4-triazole(abbreviation: p-EtTAZ); bathophenanthroline (abbreviation: BPhen);bathocuproin (abbreviation: BCP); or the like can be used. Thesubstances mentioned here mainly have an electron mobility of 10⁻⁶cm²/Vs or higher. Other substances than those may also be used for thefourth layer 106 as long as the substances have a higherelectron-transporting property than a hole-transporting property. Thefourth layer 106 may be a single layer or may be formed by stacking twoor more layers containing the above substances.

The second electrode 107 can be formed with a metal, alloy, conductivecompound, mixture of these, or the like each having a low work function(work function of 3.8 eV or lower). As a specific example of such acathode material, an element belonging to Group 1 or Group 2 in theperiodic table, i.e., an alkali metal such as lithium (Li) or cesium(Cs), an alkaline earth metal such as magnesium (Mg), calcium (Ca), orstrontium (Sr), or an alloy containing any of these (such as Mg:Ag orAl:Li) can be given. However, when a layer having a function ofpromoting electron injection is provided between the second electrode107 and the fourth layer 106 by being stacked over the second electrode107, various conductive materials such as Al, Ag, ITO, or ITO containingsilicon can be used for the second electrode 107 regardless of the workfunction.

For the layer having a function of promoting electron injection, acompound of an alkali metal or an alkaline earth metal, such as lithiumfluoride (LiF), cesium fluoride (CsF), or calcium fluoride (CaF₂) can beused. In addition, a layer which contains a substance having anelectron-transporting property in which an alkali metal or an alkalineearth metal is further contained, such as Alq containing magnesium (Mg),can be used.

The first layer 103, the second layer 104, the third layer 105, and thefourth layer 106 may be formed by other methods than the aforementionedevaporation method. For example, an ink jet method, a spin coatingmethod, or the like may be used. Moreover, a different film-formationmethod may be used for each electrode or each layer.

In the light-emitting element of the present invention having theaforementioned structure, current flows by a potential differencegenerated between the first electrode 102 and the second electrode 107and holes and electrons are recombined at the third layer 105 whichcontains the substance having a high light-emitting property, wherebylight is emitted. That is, the structure is that a light-emitting regionis formed in the third layer 105. However, it is not necessary that theentire third layer 105 functions as the light-emitting region but, forexample, the light-emitting region may be formed only in a part of thethird layer 105 that is on the second layer 104 side or the fourth layer106 side.

Light emission is extracted to the outside through one or both of thefirst electrode 102 and the second electrode 107. Therefore, one or bothof the first electrode 102 and the second electrode 107 is/are formedwith a substance having a light-transmitting property. If only the firstelectrode 102 is formed with a substance having a light-transmittingproperty, emitted light is extracted from the substrate side through thefirst electrode 102 as shown in FIG. 1A. If only the second electrode107 is formed with a substance having a light-transmitting property,emitted light is extracted from a side opposite of the substrate sidethrough the second electrode 107 as shown in FIG. 1B. If both the firstelectrode 102 and the second electrode 107 are formed with a substancehaving a light-transmitting property, emitted light is extracted fromboth the substrate side and the side opposite of the substrate sidethrough the first electrode 102 and the second electrode 107 as shown inFIG. 1C.

The structure of the layers provided between the first electrode 102 andthe second electrode 107 is not restricted to the aforementioned one.Other structures than the aforementioned one may be applied as long asthe structures are as follows: a region where holes and electrons arerecombined is provided apart from the first electrode 102 and the secondelectrode 107 so that optical quenching due to approximation of thelight-emitting region and the metal is suppressed, and moreover, thelayer containing the composite material of the first organic compoundand the inorganic compound is in contact with the layer containing thesecond organic compound not having a peak of an absorption spectrum in awavelength region of 450 to 800 nm if the second organic compound iscompounded with the inorganic compound in the composite material.

In other words, the multilayer structure of the layers is notparticularly restricted, and a layer which contains a substance having ahigh electron-transporting property, a substance having a highhole-transporting property, a substance having a high electron-injectingproperty, a substance having a high hole-injecting property, a substancehaving a bipolar property (a substance having a highelectron-transporting property and a high hole-transporting property),or the like may be freely combined with the layer containing thecomposite material of the first organic compound and the inorganiccompound and the layer containing the second organic compound not havinga peak of an absorption spectrum in a wavelength region of 450 to 800 nmif the second organic compound is compounded with the inorganic compoundin the composite material.

A light-emitting element shown in FIG. 2 has a structure in which afirst layer 303 which contains a substance having a highelectron-transporting property, a second layer 304 which contains asubstance having a high light-emitting property, a third layer 305 whichcontains a second organic compound not having a peak of an absorptionspectrum in a wavelength region of 450 to 800 nm if the second organiccompound is compounded with an inorganic compound contained in acomposite material of a fourth layer 306, the fourth layer 306containing the composite material, and a second electrode 307functioning as an anode are stacked over a first electrode 302functioning as a cathode. A reference numeral 301 denotes a substrate.

In this embodiment mode, the light-emitting element is manufactured overthe substrate made of glass, plastic, or the like. By manufacturing aplurality of such light-emitting elements over one substrate, a passivetype light-emitting device can be manufactured. The light-emittingelements may be manufactured over, for example, a thin film transistor(TFT) array substrate besides a substrate made of glass, plastic, or thelike. Thus, an active matrix type light-emitting device in which thedriving of the light-emitting element is controlled by a TFT can bemanufactured. The structure of the TFT is not particularly restricted.Either a staggered TFT or an inverted staggered TFT is applicable. Adriver circuit formed over the TFT array substrate may be formed byusing either or both of N-type TFTs and P-type TFTs. The crystallinityof a semiconductor film used for the TFT is not particularly restricted.An amorphous semiconductor film or a crystalline semiconductor film maybe used.

The light-emitting element of the present invention has the layer whichcontains the composite material of the first organic compound and theinorganic compound and the layer which contains the second organiccompound not having a peak of an absorption spectrum in a wavelengthregion of 450 to 800 nm if the second organic compound is compoundedwith the inorganic compound in the composite material.

The layer containing the composite material does not have a peak of anabsorption spectrum in a wavelength region of 450 to 800 nm. Therefore,light emitted from the light-emitting substance can be transmittedefficiently through the layer containing the composite material, andexternal extraction efficiency can be improved. That is, alight-emitting element having high luminous efficiency can be obtained.

The layer containing the second organic compound does not have a peak ofan absorption spectrum in a wavelength region of 450 to 800 nm if thesecond organic compound is compounded with the inorganic compound in thecomposite material. Therefore, even if the second organic compound andthe inorganic compound in the layer containing the composite materialexist as a composite material when the first layer 103 and the secondlayer 104 are in contact with each other and the inorganic compound inthe layer containing the composite material and the second organiccompound are in contact with each other at an interface between thelayer containing the composite material and the layer containing thesecond organic compound, light emitted from the light-emitting substanceis not absorbed and is transmitted through the composite materialefficiently. Thus, external extraction efficiency can be improved. Inother words, a light-emitting element having high luminous efficiencycan be obtained.

The layer containing the composite material of the first organiccompound and the inorganic compound has high conductivity. Therefore,lower-voltage driving of the light-emitting element can be achieved.

Since the layer containing the composite material of the organiccompound and the inorganic compound has high conductivity, even in thecase where the film containing the composite material has large filmthickness, the increase in drive voltage can be suppressed. Therefore,it becomes possible to optimize the film thickness of the layercontaining the composite material so that external light extractionefficiency is increased while suppressing the increase in drive voltage.

In addition, improvement of color purity by optical design withoutincreasing drive voltage can be achieved.

Since short-circuiting due to depression and projection on theelectrodes, shock, and the like can be prevented by increasing the filmthickness of the layer containing the composite material, alight-emitting element with high reliability can be obtained. Forexample, in contrast with the total film thickness of a layer or layersbetween the electrodes of the light-emitting element which generallyranges from 100 to 150 nm, the total film thickness of the layer or thelayers between the electrodes of the light-emitting element using thelayer containing the composite material can be made 100 to 500 nm, andpreferably 200 to 500 nm.

The layer containing the composite material used for the light-emittingelement of the present invention can have an ohmic contact with theelectrodes and has small contact resistance with the electrodes.Therefore, an electrode material can be selected without considering thework function and the like. In other words, selection range of theelectrode material can be wider.

Embodiment Mode 4

This embodiment mode will describe a light-emitting device having alight-emitting element of the present invention.

This embodiment mode will describe a light-emitting device having alight-emitting element of the present invention in a pixel portion, withreference to FIGS. 33A and 33B. FIG. 33A is a top view showing alight-emitting device while FIG. 33B is a cross-sectional view alonglines A-A′ and B-B′ of FIG. 33A. A reference numeral 601 shown with adotted line denotes a driver circuit portion (source side drivercircuit); 602, a pixel portion; and 603, a driver circuit portion (gateside driver circuit). Moreover, a reference numeral 604 denotes asealing substrate; 605, a sealing material; and 607, a space surroundedby the sealing material 605.

A leading wire 608 is to transmit a signal to be inputted to the sourceside driver circuit 601 and the gate side driver circuit 603, andreceive a video signal, a clock signal, a start signal, a reset signal,and the like from an FPC (Flexible Printed Circuit) 609, which serves asan external input terminal. Although only the FPC is shown here, thisFPC may be provided with a printed wiring board (PWB). Thelight-emitting device in this specification not only includes alight-emitting device itself but also a state where the light-emittingdevice has an FPC or a PWB attached thereto:

Next, a cross-sectional structure is described with reference to FIG.33B. Over an element substrate 610 are formed the driver circuit portionand the pixel portion. Here, the source side driver circuit 601, whichis the driver circuit portion, and one pixel in the pixel portion 602are shown.

In the source side driver circuit 601, a CMOS circuit in which ann-channel TFT 623 and a p-channel TFT 624 are combined is formed. TheTFT for forming the driver circuit may be formed by using variouscircuits such as a CMOS circuit, a PMOS circuit, or an NMOS circuit.Although this embodiment mode shows a driver-integrated type where thedriver circuit is formed over the substrate, the present invention isnot restricted to this, and the driver circuit may be formed outside thesubstrate, not over the substrate.

The pixel portion 602 is formed by a plurality of pixels each includinga switching TFT 611, a current control TFT 612, and a first electrode613 electrically connected to a drain of the current control TFT 612. Aninsulator 614 is formed so as to cover an end portion of the firstelectrode 613. Here, the insulator 614 is formed by using a positivephotosensitive acrylic resin film.

In order to improve coverage, an upper end portion or a lower endportion of the insulator 614 is formed so as to have a curved surfacewith curvature. For example, in the case of using a positivephotosensitive acrylic for the insulator 614, it is preferable that onlythe upper end portion of the insulator 614 have a curved surface withcurvature (a radius of curvature of 0.2 to 3 μm). As the insulator 614,either a negative type which becomes insoluble in etchant by irradiationwith light or a positive type which becomes soluble in etchant byirradiation with light can be used.

Over the first electrode 613, a layer 616 containing a light-emittingsubstance and a second electrode 617 are formed. Here, the firstelectrode 613 functioning as an anode can be formed with various metals,alloys, conductive compounds, or mixture thereof. If the first electrodeis used as an anode, it is preferable to use, among those materials, amaterial having a high work function (work function of 4.0 eV orhigher), or the like. For example, a single layer of indium tin oxidecontaining silicon, indium zinc oxide (IZO) in which zinc oxide (ZnO) ismixed by 2 to 20 wt % into indium oxide, a titanium nitride film, achromium film, a tungsten film, a Zn film, a Pt film, or the like can beused. Moreover, a multilayer including a film containing titaniumnitride and a film containing aluminum as its main component; athree-layer structure including a titanium nitride film, a filmcontaining aluminum as its main component, and a titanium nitride film;or the like can be used. The multilayer structure achieves to have lowwiring resistance, favorable ohmic contact, and a function as an anode.

The layer 616 containing a light-emitting substance is formed by variousmethods such as an evaporation method using an evaporation mask, an inkjet method, a spin coating method, and the like. The layer 616containing a light-emitting substance has the layer containing thecomposite material shown in Embodiment Mode 1 and the layer containingthe second organic compound shown in Embodiment Mode 2. As anothermaterial that constitutes a part of the layer 616 containing alight-emitting substance, a low molecular material, a medium molecularmaterial (including oligomer and dendrimer), or a high molecularmaterial may be used. As the material for the layer containing alight-emitting substance, generally an organic compound is often used asa single layer or a multilayer; however, in the present invention, astructure using an inorganic compound as a part of a film containing anorganic compound is also acceptable.

As the material for the second electrode 617 functioning as a cathode,which is formed over the layer 616 containing a light-emittingsubstance, a metal, alloy, conductive compound, mixture of these, or thelike each having a low work function (work function of 3.8 eV or lower)can be used. As a specific example of such a cathode material, anelement belonging to Group 1 or Group 2 in the periodic table, i.e., analkali metal such as lithium (Li) or cesium (Cs), an alkaline earthmetal such as magnesium (Mg), calcium (Ca), or strontium (Sr), or analloy containing any of these (such as Mg:Ag or Al:Li) can be given. Inthe case where light generated in the layer 616 containing alight-emitting substance is transmitted through the second electrode617, the second electrode 617 is preferably formed by using a multilayerof a metal thin film and a transparent conductive film (ITO, indiumoxide containing 2 to 20 wt % of zinc oxide, indium tin oxide containingsilicon, zinc oxide (ZnO), or the like).

When the sealing substrate 604 and the element substrate 610 areattached to each other by the sealing material 605, the light-emittingelement 618 is provided in the space 607 surrounded by the elementsubstrate 610, the sealing substrate 604, and the sealing material 605.The space 607 may be filled with filler, and may be filled with an inertgas (such as nitrogen or argon), the sealing material 605, or the like.

An epoxy-based resin is preferable for the sealing material 605. Thematerial preferably allows as little moisture and oxygen as possible topenetrate. As a material for the sealing substrate 604, a plasticsubstrate made of FRP (Fiberglass-Reinforced Plastics), PVF (polyvinylfluoride), Mylar, polyester, acrylic, or the like can be used besides aglass substrate or a quartz substrate.

In this way, the light-emitting device having the light-emitting elementof the present invention can be obtained.

The light-emitting device of the present invention has the layercontaining the composite material shown in Embodiment Mode 1 and thelayer containing the second organic compound shown in Embodiment Mode 2,which is provided so as to be in contact with the layer containing thecomposite material. Therefore, light emitted from the light-emittingregion can be extracted to the outside efficiently, and the luminousefficiency is high. Moreover, the drive voltage can be decreased,thereby allowing lower power consumption.

Moreover, the light-emitting device of the present invention cansuppress the increase in drive voltage even though the layer containingthe composite material is made thicker. Therefore, the short-circuitingof the light-emitting element can be prevented by increasing thethickness of the layer containing the composite material. Moreover,improvement of external extraction efficiency of light emission can beachieved by optical design. Thus, a highly-reliable light-emittingdevice with low power consumption can be obtained.

Although this embodiment mode has described the active matrix typelight-emitting device in which the driving of the light-emitting elementis controlled by the transistor, the light-emitting device may be of apassive type in which the light-emitting element is driven withoutparticularly providing the element for driving, such as the transistor.FIG. 34 is a perspective view of a passive type light-emitting devicemanufactured by applying the present invention. In FIG. 34, a layer 955containing a light-emitting substance is provided between an electrode952 and an electrode 956 over a substrate 951. An end portion of theelectrode 952 is covered with an insulating layer 953. Then, over theinsulating layer 953 is provided a partition wall layer 954. A side wallof the partition wall layer 954 has such a gradient that the distancebetween one side wall and the other side wall becomes shorter asapproaching the substrate surface. That is to say, a cross section ofthe partition wall layer 954 in a short-side direction istrapezoid-like, in which a bottom side (a side in a similar direction toa surface direction of the insulating layer 953, which has contact withthe insulating layer 953) is shorter than an upper side (a side in asimilar direction to the surface direction of the insulating layer 953,which does not have contact with the insulating layer 953). In this way,by providing the partition wall layer 954, a problem of a light-emittingelement due to electrostatic and the like can be prevented. Moreover,even a passive type light-emitting device can be driven with low powerconsumption by including a light-emitting element of the presentinvention that has high luminous efficiency and that is driven with lowdrive voltage.

Embodiment Mode 5

This embodiment mode will describe an electronic appliance of thepresent invention, which includes the light-emitting device shown inEmbodiment Mode 4 as a part thereof. The electronic appliance of thepresent invention has a display portion of low power consumption, andhas the layer containing the composite material shown in Embodiment Mode1 and the layer containing the second organic compound shown inEmbodiment Mode 2, which is provided so as to be in contact with thelayer containing the composite material. By increasing the thickness ofthe layer containing the composite material shown in Embodiment Mode 1,it is also possible to provide an electronic appliance having a displayportion with high reliability in which short-circuiting due to shockfrom the outside, a minute foreign particle, or the like is suppressed.

As the electronic appliance manufactured by using the light-emittingdevice of the present invention, a camera such as a video camera or adigital camera, a goggle-type display, a navigation system, a soundreproducing device (such as a car audio component or an audiocomponent), a computer, a game machine, a mobile information terminal (amobile computer, a mobile phone, a mobile game machine, or an electronicbook), an image reproducing device equipped with a recording medium(specifically, a device equipped with a display device for reproducing arecording medium such as digital versatile disk (DVD) and displaying theimage), and the like are given. Specific examples of these electronicappliances are shown in FIGS. 35A to 35D. FIG. 35A shows a televisiondevice according to the present invention, which includes a housing9101, a supporter 9102, a display portion 9103, a speaker portion 9104,a video input terminal 9105, and the like. In this television device,the display portion 9103 is formed by arranging similar light-emittingelements to those described in Embodiment Modes 2 to 6 in a matrix form.The light-emitting elements have advantages of their high luminousefficiency and low drive voltage. Moreover, it is possible to preventshort-circuiting due to minute foreign particles, shock from theoutside, and the like. Since the display portion 9103 having suchlight-emitting elements also has similar advantages, this televisiondoes not deteriorate in its image quality and consumes less electricpower. Since the number of circuits each having adeterioration-compensation function and power source circuits can bedrastically decreased or the size of such circuits can be reduced in thetelevision device because of such advantages, reduction in size andweight of the housing 9101 and the supporter 9102 can be achieved. Sincereduction in size, weight, and power consumption, and moreoverimprovement of image quality can be achieved in the television device ofthe present invention, products suitable for dwelling environment can beprovided.

FIG. 35B shows a computer according to the present invention, whichincludes a main body 9201, a housing 9202, a display portion 9203, akeyboard 9204, an external connection port 9205, a pointing mouse 9206,and the like. In this computer, the display portion 9203 is formed byarranging similar light-emitting elements to those described inEmbodiment Modes 2 to 6 in a matrix form. The light-emitting elementshave advantages of their high luminous efficiency and low drive voltage.Moreover, it is possible to prevent short-circuiting due to minuteforeign particles, shock from the outside, and the like. Since thedisplay portion 9203 having such light-emitting elements also hassimilar advantages, this computer does not deteriorate in its imagequality and consumes less electric power. Since the number of circuitseach having a deterioration-compensation function and power sourcecircuits can be drastically decreased or the size of such circuits canbe reduced in the computer because of such advantages, reduction in sizeand weight of the main body 9201 and the housing 9202 can be achieved.Since reduction in size, weight, and power consumption, and moreoverimprovement of image quality can be achieved in the computer of thepresent invention, products suitable for dwelling environment can beprovided. Furthermore, it becomes possible to carry around the computer,and the computer having a display portion which resists shock from theoutside when carrying it around can be provided.

FIG. 35C shows a mobile phone of the present invention, which includes amain body 9401, a housing 9402, a display portion 9403, an audio inputportion 9404, an audio output portion 9405, an operation key 9406, anexternal connection port 9407, an antenna 9408, and the like. Thisdisplay portion 9403 is formed by arranging similar light-emittingelements to those described in Embodiment Modes 2 to 6 in a matrix form.The light-emitting elements have advantages of their high luminousefficiency and low drive voltage. Moreover, it is possible to preventshort-circuiting due to minute foreign particles, shock from theoutside, and the like. Since the display portion 9403 having suchlight-emitting elements also has similar advantages, this mobile phonedoes not deteriorate in its image quality and consumes less electricpower. Since the number of circuits each having adeterioration-compensation function and power source circuits can bedrastically decreased or the size of such circuits can be reduced in themobile phone because of such advantages, reduction in size and weight ofthe main body 9401 and the housing 9402 can be achieved. Since reductionin size, weight, and power consumption, and moreover improvement ofimage quality can be achieved in the mobile phone of the presentinvention, products suitable for being carried around can be provided.In addition, products having display portions which resist shock fromthe outside when being carried around can be provided.

FIG. 35D shows a camera of the present invention, which includes a mainbody 9501, a display portion 9502, a housing 9503, an externalconnection port 9504, a remote control receiving portion 9505, an imagereceiving portion 9506, a battery 9507, an audio input portion 9508, anoperation key 9509, an eyepiece portion 9510, and the like. In thiscamera, the display portion 9502 is formed by arranging similarlight-emitting elements to those described in Embodiment Modes 2 to 6 ina matrix form. The light-emitting elements have advantages of their highluminous efficiency and low drive voltage. Moreover, it is possible toprevent short-circuiting due to minute foreign particles, shock from theoutside, and the like. Since the display portion 9502 having suchlight-emitting elements also has similar advantages, this camera doesnot deteriorate in its image quality and consumes less electric power.Since the number of circuits each having a deterioration-compensationfunction and power source circuits can be drastically decreased or thesize of such circuits can be reduced in the camera because of suchadvantages, reduction in size and weight of the main body 9501 can beachieved. Since reduction in size, weight, and power consumption, andmoreover improvement of image quality can be achieved in the camera ofthe present invention, products suitable for being carried around can beprovided. In addition, products having display portions which resistshock from the outside when carrying them around can be provided.

As thus described, application range of the light-emitting device of thepresent invention is quite wide, and this light-emitting device can beapplied to electronic appliances of every field. By using thelight-emitting device of the present invention, an electronic appliancehaving a highly-reliable display portion consuming less electric powercan be provided.

Moreover, the light-emitting device of the present invention has thelight-emitting element having high luminous efficiency, and thelight-emitting device can be used as an illumination device. An exampleof using the light-emitting element of the present invention as anillumination device will be described with reference to FIG. 36.

FIG. 36 shows an example of a liquid crystal display device in which thelight-emitting device of the present invention is used as a backlight.The liquid crystal display device shown in FIG. 36 includes a housing901, a liquid crystal layer 902, a backlight 903, and a housing 904, inwhich the liquid crystal layer 902 is connected to a driver IC 905. Thebacklight 903 uses the light-emitting device of the present invention,and current is supplied to the backlight 903 by a terminal 906.

When the light-emitting device of the present invention is used as thebacklight of the liquid crystal display device, the backlight consumesless electric power. Moreover, since the light-emitting device of thepresent invention is an illumination device of surface light emissionand the enlargement of the light-emitting device is possible, thebacklight can be made larger and the liquid crystal display device canalso have a larger area. Moreover, since the light-emitting device isthin and consumes less electric power, reduction in thickness and powerconsumption of the display device is possible.

Embodiment 1

This embodiment will describe optical characteristics and a method formanufacturing an organic compound, an inorganic compound, and a layercontaining a composite material which are used for a light-emittingelement of the present invention.

Sample 1

First, a quartz substrate is fixed at a substrate holder in a vacuumevaporation apparatus. Then, DNTPD and molybdenum oxide (VI) wereseparately put in different resistance-heating evaporation sources, andthe vacuum apparatus was evacuated to reduce pressure to be about 10⁻⁴Pa. After that, a layer containing DNTPD and molybdenum oxide was formedby a co-evaporation method. At this time, the co-evaporation was carriedout so that the weight ratio between DNTPD and molybdenum oxide was 2:1.The thickness of the layer was set to 100 nm.

A measurement result of an absorption spectrum of a DNTPD-molybdenumoxide composite layer (Sample 1) formed in this way in a wavelengthregion of 450 to 800 nm is shown in FIG. 37. Further, the transmittancethereof is shown in FIG. 4.

Comparative Example 1 Comparative Sample 2

First, a quartz substrate is fixed at a substrate holder in a vacuumevaporation apparatus. Then, NPB and molybdenum oxide (VI) wereseparately put in different resistance-heating evaporation sources, andthe vacuum apparatus was evacuated to reduce pressure to be about 10⁻⁴Pa. After that, a layer containing NPB and molybdenum oxide was formedby a co-evaporation method. At this time, the co-evaporation was carriedout so that the weight ratio between NPB and molybdenum oxide was2:0.75. The thickness of the layer was set to 100 nm

A measurement result of an absorption spectrum of a NPB-molybdenum oxidecomposite layer (Comparative Sample 2) formed in this way in awavelength region of 450 to 800 nm is shown in FIG. 37. Further, thetransmittance thereof is shown in FIG. 4.

As can be seen from FIG. 4 and FIG. 37, the DNTPD-molybdenum oxidecomposite layer does not have an absorption peak but has a transmittanceof 80% or higher in a wavelength region of 450 to 800 nm. In contrast,the NPB-molybdenum oxide composite layer as the comparative example hasan absorption peak at a wavelength of about 500 nm and has a wavelengthregion in which the transmittance is less than 80%.

Therefore, it is understood that the composite material of the presentinvention and the layer containing the organic compound, which isprovided so as to be in contact with the composite material do not havean absorption peak but have high transmittance in a wavelength region of450 to 800 nm.

Embodiment 2

This embodiment will describe optical characteristics and a method formanufacturing an organic compound, an inorganic compound, and a layercontaining a composite material which are used for a light-emittingelement of the present invention.

Sample 3

First, a quartz substrate is fixed at a substrate holder in a vacuumevaporation apparatus. Then, t-BuDNA and molybdenum oxide (VI) wereseparately put in different resistance-heating evaporation sources, andthe vacuum apparatus was evacuated to reduce pressure to be about 10⁻⁴Pa. After that, a layer containing t-BuDNA and molybdenum oxide wasformed by a co-evaporation method. At this time, the co-evaporation wascarried out so that the weight ratio between t-BuDNA and molybdenumoxide was 2:1. The thickness of the layer was set to 100 nm.

Sample 4

Similarly to Sample 3, a quartz substrate is fixed at a substrate holderin a vacuum evaporation apparatus. Then, DPPA and molybdenum oxide (VI)were separately put in different resistance-heating evaporation sources,and the vacuum apparatus was evacuated to reduce pressure to be about10⁻⁴ Pa. After that, a layer containing DPPA and molybdenum oxide wasformed by a co-evaporation method. At this time, the co-evaporation wascarried out so that the weight ratio between DPPA and molybdenum oxidewas 2:1. The thickness of the layer was set to 100 nm.

Sample 5

Similarly to Sample 3, a quartz substrate is fixed at a substrate holderin a vacuum evaporation apparatus. Then, DNA and molybdenum oxide (VI)were separately put in different resistance-heating evaporation sources,and the vacuum apparatus was evacuated to reduce pressure to be about10⁻⁴ Pa. After that, a layer containing DNA and molybdenum oxide wasformed by a co-evaporation method. At this time, the co-evaporation wascarried out so that the weight ratio between DNA and molybdenum oxidewas 2:1. The thickness of the layer was set to 100 nm.

Sample 6

Similarly to Sample 3, a quartz substrate is fixed at a substrate holderin a vacuum evaporation apparatus. Then, DPAnth and molybdenum oxide(VI) were separately put in different resistance-heating evaporationsources, and the vacuum apparatus was evacuated to reduce pressure to beabout 10⁻⁴ Pa. After that, a layer containing DPAnth and molybdenumoxide was formed by a co-evaporation method. At this time, theco-evaporation was carried out so that the weight ratio between DPAnthand molybdenum oxide was 2:1. The thickness of the layer was set to 100nm.

Measurement results of absorption spectra of the t-BuDNA-molybdenumoxide composite layer (Sample 3), the DPPA-molybdenum oxide compositelayer (Sample 4), the DNA-molybdenum oxide composite layer (Sample 5),and the DPAnth-molybdenum oxide composite layer (Sample 6) formed inthis way, in a wavelength region of 450 to 800 nm are shown in FIG. 38.Further, the transmittance of each layer is shown in FIG. 5.

As can be seen from FIG. 5 and FIG. 38, the t-BuDNA-molybdenum oxidecomposite layer (Sample 3), the DPPA-molybdenum oxide composite layer(Sample 4), the DNA-molybdenum oxide composite layer (Sample 5), and theDPAnth-molybdenum oxide composite layer (Sample 6) do not have anabsorption peak but have a transmittance of 80% or higher in awavelength region of 450 to 800 nm.

Therefore, it is understood that the layer containing the compositematerial of the present invention and the layer containing the organiccompound, which is provided so as to be in contact with the compositematerial do not have an absorption peak but have high transmittance in awavelength region of 450 to 800 nm.

The layer containing the organic compound has higher transmittance thanthe layer containing the composite material. Therefore, it is understoodthat a multilayer body of the layer containing the composite materialand the layer containing the organic compound, which is provided so asto be in contact with the composite material has a transmittance higherthan 80%.

Moreover, the relation between the absorbance and the film thickness isrepresented by the following formula (2) according to Lambert-Beer'slaw.

$\begin{matrix}{A = {{\log \frac{I_{0}}{I}} = {ɛ\; L}}} & (2)\end{matrix}$

-   -   A: absorbance    -   I_(o): incident light    -   I: transmitted light    -   ε: absorbance coefficient per unit of film thickness (nm⁻¹)    -   L: thickness (nm)

Moreover, the transmittance is represented by the following formula (3).

$\begin{matrix}{T - \frac{I}{I_{0}}} & (3)\end{matrix}$

-   -   T: transmittance

The absorbance is represented by the following formula (4) by assigningthe formula (3) to the formula (2).

$\begin{matrix}{{{\log \frac{1}{T}} = {ɛ\; L}}{ɛ = {{\frac{1}{L} \cdot \log}\frac{1}{T}}}} & (4)\end{matrix}$

For example, the absorbance coefficient per unit of film thickness isrepresented by the formula (5) when the film thickness L is 100 nm andthe transmittance T is 80%.

$\begin{matrix}{{ɛ \leqq {{\frac{1}{100} \cdot \log}\frac{1}{0.8}}}{{ɛ \leqq {\frac{1}{100} \cdot 0.097}} = {9.7 \times 10^{- 4}}}} & (5)\end{matrix}$

It is preferable that the composite material used for the light-emittingelement of the present invention have a transmittance of 80% or higherin a wavelength region of 450 to 800 nm. That is, the following formula(6) is preferably satisfied.

A=εl≦9.7×10⁻⁴ ×l  (6)

-   -   A: absorbance    -   l: thickness (nm)

If the transmittance is 0%, for example in the case of using areflective material or the like, Lambert-Beer's law is not effective;therefore, the formula (6) is not satisfied.

Embodiment 3

This embodiment will describe a light-emitting element of the presentinvention more specifically.

First, indium tin oxide containing silicon oxide was formed over a glasssubstrate by a sputtering method, thereby forming a first electrode. Thefilm thickness thereof was set to 110 nm with an electrode area of 2mm×2 mm.

Next, the substrate where the first electrode was formed was fixed at asubstrate holder provided in a vacuum evaporation apparatus so that asurface of the substrate at which the first electrode was formed facesdownward. After that, the vacuum apparatus was evacuated to reducepressure to be about 10⁻⁴ Pa, and then t-BuDNA and molybdenum oxide (VI)were co-evaporated over the first electrode, thereby forming a layercontaining a composite material. The film thickness was set to 50 nm,and the volume ratio between t-BuDNA and molybdenum oxide (VI) wasadjusted so that molybdenum oxide was contained by 10 vol %. Aco-evaporation method is an evaporation method by which evaporation iscarried out from a plurality of evaporation sources at the same timewithin one process chamber.

Next, t-BuDNA was formed by an evaporation method using resistanceheating so as to be in contact with the layer containing the compositematerial in 10 nm thick. The ionization potential of t-BuDNA was 5.55eV.

By co-evaporating Alq and DPQd, a 40-nm-thick light-emitting layer wasformed over t-BuDNA. Here, the weight ratio between Alq and DPQd wasadjusted so as to be 1:0.005 (=Alq:DPQd). Thus, DPQd exists in such astate that DPQd disperses in a layer containing Alq.

After that, Alq was formed to have a thickness of 30 nm over thelight-emitting layer by an evaporation method by resistance heating,thereby forming an electron-transporting layer.

Further, lithium fluoride was formed in 1 nm thick over theelectron-transporting layer by an evaporation method by resistanceheating, thereby forming an electron-injecting layer.

Finally, aluminum was formed in 200 nm thick over the electron-injectinglayer by an evaporation method by resistance heating, thereby forming asecond electrode. Thus, a light-emitting element 1 was manufactured.

Comparative Example 2

First, indium tin oxide containing silicon oxide was formed over a glasssubstrate by a sputtering method, thereby forming a first electrode. Thefilm thickness thereof was set to 110 nm with an electrode area of 2mm×2 mm.

Next, the substrate where the first electrode was formed was fixed at asubstrate holder provided in a vacuum evaporation apparatus so that asurface of the substrate at which the first electrode was formed facesdownward. After that, the vacuum apparatus was evacuated to reducepressure to be about 10⁻⁴ Pa, and then t-BuDNA and molybdenum oxide (VI)were co-evaporated over the first electrode, thereby forming a layercontaining a composite material. The film thickness was set to 50 nm,and the volume ratio between t-BuDNA and molybdenum oxide (VI) wasadjusted so that molybdenum oxide was contained by 10 vol %. Aco-evaporation method is an evaporation method by which evaporation iscarried out from a plurality of evaporation sources at the same timewithin one process chamber.

Next, NPB was formed in 10 nm thick by an evaporation method usingresistance heating.

Moreover, by co-evaporating Alq and DPQd, a 40-nm-thick light-emittinglayer was formed over NPB. Here, the weight ratio between Alq and DPQdwas adjusted so as to be 1:0.005 (=Alq:DPQd). Thus, DPQd exists in sucha state that DPQd disperses in a layer including Alq.

After that, Alq was formed in 30 nm thick over the light-emitting layerby an evaporation method by resistance heating, thereby forming anelectron-transporting layer.

Further, lithium fluoride was formed in 1 nm thick over theelectron-transporting layer by an evaporation method by resistanceheating, thereby forming an electron-injecting layer.

Finally, aluminum was formed in 200 nm thick over the electron-injectinglayer by an evaporation method by resistance heating, thereby forming asecond electrode. Thus, a comparative light-emitting element 1 wasmanufactured.

Current-voltage characteristics of the light-emitting element 1manufactured in Embodiment 3 and the comparative light-emitting element1 manufactured in Comparative Example 2 are shown in FIG. 6. Moreover,luminance-voltage characteristics thereof are shown in FIG. 7. Further,current efficiency-luminance characteristics thereof are shown in FIG.8.

In the light-emitting element 1, the voltage required to obtain aluminance of 1226 cd/m² was 5.6 V, at which current flowed for 0.35 mA(with a current density of 8.63 mA/cm²). Moreover, the currentefficiency at this time was 14.2 cd/A Meanwhile, in the comparativelight-emitting element 1, the voltage required to obtain a luminance of1096 cd/m² was 5.8 V, at which current flowed for 0.34 mA (with acurrent density of 8.57 mA/cm²). The current efficiency at this time was12.8 cd/A.

The light-emitting element 1 and the comparative light-emitting element1 have almost the same current-voltage characteristics. However, sincethe current efficiency-luminance characteristics of the light-emittingelement 1 have improved, it is understood that the luminance-voltagecharacteristics have also improved. In other words, it is understoodthat the voltage required to obtain a certain luminance has decreased.

From the above results, it has been confirmed that luminous efficiencyis improved by applying the present invention.

Embodiment 4

This embodiment will describe a light-emitting element of the presentinvention more specifically.

First, indium tin oxide containing silicon oxide was formed over a glasssubstrate by a sputtering method, thereby forming a first electrode. Thefilm thickness thereof was set to 110 nm with an electrode area of 2mm×2 mm.

Next, the substrate where the first electrode was formed was fixed at asubstrate holder provided in a vacuum evaporation apparatus so that asurface of the substrate at which the first electrode was formed facesdownward. After that, the vacuum apparatus was evacuated to reducepressure to be about 10⁻⁴ Pa, and then t-BuDNA and molybdenum oxide (VI)were co-evaporated over the first electrode, thereby forming a layercontaining a composite material. The film thickness was set to 50 nm,and the volume ratio between t-BuDNA and molybdenum oxide (VI) wasadjusted so that molybdenum oxide was contained by 10 vol %. Aco-evaporation method is an evaporation method by which evaporation iscarried out from a plurality of evaporation sources at the same timewithin one process chamber.

Next, t-BuDNA was formed in 10 nm thick by an evaporation method usingresistance heating so as to be in contact with the layer containing thecomposite material. The ionization potential of t-BuDNA was 5.55 eV.

By co-evaporating Alq and DPQd, a 40-nm-thick light-emitting layer wasformed over t-BuDNA. Here, the weight ratio between Alq and DPQd wasadjusted so as to be 1:0.005 (=Alq:DPQd). Thus, DPQd exists in such astate that DPQd disperses in a layer including Alq.

After that, BPhen was formed in 30 nm thick over the light-emittinglayer by an evaporation method by resistance heating, thereby forming anelectron-transporting layer.

Further, lithium fluoride was formed in 1 nm thick over theelectron-transporting layer by an evaporation method by resistanceheating, thereby forming an electron-injecting layer.

Finally, aluminum was formed in 200 nm thick over the electron-injectinglayer by an evaporation method by resistance heating, thereby forming asecond electrode. Thus, a light-emitting element 2 was manufactured.

Comparative Example 3

First, indium tin oxide containing silicon oxide was formed over a glasssubstrate by a sputtering method, thereby forming a first electrode. Thefilm thickness thereof was set to 110 nm with an electrode area of 2mm×2 mm.

Next, the substrate where the first electrode was formed was fixed at asubstrate holder provided in a vacuum evaporation apparatus so that asurface of the substrate at which the first electrode was formed facesdownward. After that, the vacuum apparatus was evacuated to reducepressure to be about 10⁻⁴ Pa, and then t-BuDNA and molybdenum oxide (VI)were co-evaporated over the first electrode, thereby forming a layercontaining a composite material. The film thickness was set to 50 nm,and the volume ratio between t-BuDNA and molybdenum oxide (VI) wasadjusted so that molybdenum oxide was contained by 10 vol %. Aco-evaporation method is an evaporation method by which evaporation iscarried out from a plurality of evaporation sources at the same timewithin one process chamber.

Next, NPB was formed in 10 nm thick by an evaporation method usingresistance heating.

By co-evaporating Alq and DPQd, a 40-nm-thick light-emitting layer wasformed over NPB. Here, the weight ratio between Alq and DPQd wasadjusted so as to be 1:0.005 (=Alq:DPQd). Thus, DPQd exists in such astate that DPQd disperses in a layer including Alq.

After that, BPhen was formed in 30 nm thick over the light-emittinglayer by an evaporation method by resistance heating, thereby forming anelectron-transporting layer.

Further, lithium fluoride was formed in 1 nm thick over theelectron-transporting layer by an evaporation method by resistanceheating, thereby forming an electron-injecting layer.

Finally, aluminum was formed in 200 nm thick over the electron-injectinglayer by an evaporation method by resistance heating, thereby forming asecond electrode. Thus, a comparative light-emitting element 2 wasmanufactured.

Current-voltage characteristics of the light-emitting element 2manufactured in Embodiment 4 and the comparative light-emitting element2 manufactured in Comparative Example 3 are shown in FIG. 9. Moreover,luminance-voltage characteristics thereof are shown in FIG. 10. Further,current efficiency-luminance characteristics thereof are shown in FIG.11.

In the light-emitting element 2, the voltage required to obtain aluminance of 1233 cd/m² was 4.6 V, at which current flowed for 0.36 mA(with a current density of 8.90 mA/cm²). Moreover, the currentefficiency at this time was 13.9 cd/A. Meanwhile, in the comparativelight-emitting element 2, the voltage required to obtain a luminance of1179 cd/m² was 4.8 V, at which current flowed for 0.38 mA (with acurrent density of 9.59 mA/cm²). The current efficiency at this time was12.3 cd/A.

The light-emitting element 2 and the comparative light-emitting element2 have almost the same current-voltage characteristics. However, sincethe current efficiency-luminance characteristics of the light-emittingelement 2 have improved, it is understood that the luminance-voltagecharacteristics have also improved. In other words, it is understoodthat the voltage required to obtain a certain luminance has decreased.

From the above results, it has been confirmed that luminous efficiencyis improved by applying the present invention.

Embodiment 5

This embodiment will describe a light-emitting element of the presentinvention more specifically.

First, indium tin oxide containing silicon oxide was formed over a glasssubstrate by a sputtering method, thereby forming a first electrode. Thefilm thickness thereof was set to 110 nm with an electrode area of 2mm×2 mm.

Next, the substrate where the first electrode was formed was fixed at asubstrate holder provided in a vacuum evaporation apparatus so that asurface of the substrate at which the first electrode was formed facesdownward. After that, the vacuum apparatus was evacuated to reducepressure to be about 10⁻⁴ Pa, and then t-BuDNA and molybdenum oxide (VI)were co-evaporated over the first electrode, thereby forming a layercontaining a composite material. The film thickness was set to 50 nm,and the volume ratio between t-BuDNA and molybdenum oxide (VI) wasadjusted so that molybdenum oxide was contained by 10 vol %. Aco-evaporation method is an evaporation method by which evaporation iscarried out from a plurality of evaporation sources at the same timewithin one process chamber.

Next, t-BuDBA was formed in 10 nm thick by an evaporation method usingresistance heating so as to be in contact with the layer containing thecomposite material.

By co-evaporating Alq and DPQd further, a 40-nm-thick light-emittinglayer was formed over t-BuDBA. Here, the weight ratio between Alq andDPQd was adjusted so as to be 1:0.005 (=Alq:DPQd). Thus, DPQd exists insuch a state that DPQd disperses in a layer including Alq.

After that, Alq was formed to have a thickness of 30 nm over thelight-emitting layer by an evaporation method by resistance heating,thereby forming an electron-transporting layer.

Further, lithium fluoride was formed in 1 nm thick over theelectron-transporting layer by an evaporation method by resistanceheating, thereby forming an electron-injecting layer.

Finally, aluminum was formed in 200 nm thick over the electron-injectinglayer by an evaporation method by resistance heating, thereby forming asecond electrode. Thus, a light-emitting element 3 was manufactured.

Comparative Example 4

First, indium tin oxide containing silicon oxide was formed over a glasssubstrate by a sputtering method, thereby forming a first electrode. Thefilm thickness thereof was set to 110 nm with an electrode area of 2mm×2 mm.

Next, the substrate where the first electrode was formed was fixed at asubstrate holder provided in a vacuum evaporation apparatus so that asurface of the substrate at which the first electrode was formed facesdownward. After that, the vacuum apparatus was evacuated to reducepressure to be about 10⁻⁴ Pa, and then t-BuDNA and molybdenum oxide (VI)were co-evaporated over the first electrode, thereby forming a layercontaining a composite material. The film thickness was set to 50 nm,and the volume ratio between t-BuDNA and molybdenum oxide (VI) wasadjusted so that molybdenum oxide was contained by 10 vol %. Aco-evaporation method is an evaporation method by which evaporation iscarried out from a plurality of evaporation sources at the same timewithin one process chamber.

Next, NPB was formed in 10 nm thick by an evaporation method usingresistance heating.

By co-evaporating Alq and DPQd further, a 40-nm-thick light-emittinglayer was formed over NPB. Here, the weight ratio between Alq and DPQdwas adjusted so as to be 1:0.005 (=Alq:DPQd). Thus, DPQd exists in sucha state that DPQd disperses in a layer including Alq.

After that, Alq was formed to have a thickness of 30 nm over thelight-emitting layer by an evaporation method by resistance heating,thereby forming an electron-transporting layer.

Further, lithium fluoride was formed in 1 nm thick over theelectron-transporting layer by an evaporation method by resistanceheating, thereby forming an electron-injecting layer.

Finally, aluminum was formed in 200 nm thick over the electron-injectinglayer by an evaporation method by resistance heating, thereby forming asecond electrode. Thus, a comparative light-emitting element 3 wasmanufactured.

Current-voltage characteristics of the light-emitting element 3manufactured in Embodiment 5 and the comparative light-emitting element3 manufactured in Comparative Example 4 are shown in FIG. 12. Moreover,luminance-voltage characteristics thereof are shown in FIG. 13. Further,current efficiency-luminance characteristics thereof are shown in FIG.14.

In the light-emitting element 3, the voltage required to obtain aluminance of 1063 cd/m² was 5.6 V, at which current flowed for 0.31 mA(with a current density of 7.65 mA/cm²). Moreover, the currentefficiency at this time was 13.9 cd/A. Meanwhile, in the comparativelight-emitting element 3, the voltage required to obtain a luminance of1027 cd/mr² was 5.8 V, at which current flowed for 0.32 mA (with acurrent density of 8.11 mA/cm²). The current efficiency at this time was12.7 cd/A.

The light-emitting element 3 and the comparative light-emitting element3 have almost the same current-voltage characteristics. However, sincethe current efficiency-luminance characteristics of the light-emittingelement 3 have improved, it is understood that the luminance-voltagecharacteristics have also improved. In other words, it is understoodthat the voltage required to obtain a certain luminance has decreased.

From the above results, it has been confirmed that luminous efficiencyis improved by applying the present invention.

Embodiment 6

This embodiment will describe a light-emitting element of the presentinvention more specifically.

First, indium tin oxide containing silicon oxide was formed over a glasssubstrate by a sputtering method, thereby forming a first electrode. Thefilm thickness thereof was set to 110 nm with an electrode area of 2mm×2 mm.

Next, the substrate where the first electrode was formed was fixed at asubstrate holder provided in a vacuum evaporation apparatus so that asurface of the substrate at which the first electrode was formed facesdownward. After that, the vacuum apparatus was evacuated to reducepressure to be about 10⁻⁴ Pa, and then t-BuDBA and molybdenum oxide (VI)were co-evaporated over the first electrode, thereby forming a layercontaining a composite material. The film thickness was set to 50 nm,and the volume ratio between t-BuDBA and molybdenum oxide (VI) wasadjusted so that molybdenum oxide was contained by 10 vol %. Aco-evaporation method is an evaporation method by which evaporation iscarried out from a plurality of evaporation sources at the same timewithin one process chamber.

Next, t-BuDBA was formed in 10 nm thick by an evaporation method usingresistance heating so as to be in contact with the layer containing thecomposite material.

By co-evaporating Alq and DPQd, a 40-nm-thick light-emitting layer wasformed over t-BuDBA. Here, the weight ratio between Alq and DPQd wasadjusted so as to be 1:0.005 (=Alq:DPQd). Thus, DPQd exists in such astate that DPQd disperses in a layer including Alq.

After that, Alq was formed to have a thickness of 30 nm over thelight-emitting layer by an evaporation method by resistance heating,thereby forming an electron-transporting layer.

Further, lithium fluoride was formed in 1 nm thick over theelectron-transporting layer by an evaporation method by resistanceheating, thereby forming an electron-injecting layer.

Finally, aluminum was formed in 200 nm thick over the electron-injectinglayer by an evaporation method by resistance heating, thereby forming asecond electrode. Thus, a light-emitting element 4 was manufactured.

Comparative Example 5

First, indium tin oxide containing silicon oxide was formed over a glasssubstrate by a sputtering method, thereby forming a first electrode. Thefilm thickness thereof was set to 110 nm with an electrode area of 2mm×2 mm.

Next, the substrate where the first electrode was formed was fixed at asubstrate holder provided in a vacuum evaporation apparatus so that asurface of the substrate at which the first electrode was formed facesdownward. After that, the vacuum apparatus was evacuated to reducepressure to be about 10⁻⁴ Pa, and then t-BuDBA and molybdenum oxide (VI)were co-evaporated over the first electrode, thereby forming a layercontaining a composite material. The film thickness was set to 50 nm,and the volume ratio between t-BuDBA and molybdenum . . . oxide (VI) wasadjusted so that molybdenum oxide was contained by 10 vol %. Aco-evaporation method is an evaporation method by which evaporation iscarried out from a plurality of evaporation sources at the same timewithin one process chamber.

Next, NPB was formed in 10 nm thick by an evaporation method usingresistance heating.

By co-evaporating Alq and DPQd, a 40-nm-thick light-emitting layer wasformed over NPB. Here, the weight ratio between Alq and DPQd wasadjusted so as to be 1:0.005 (=Alq:DPQd). Thus, DPQd exists in such astate that DPQd disperses in a layer including Alq.

After that, Alq was formed to have a thickness of 30 nm over thelight-emitting layer by an evaporation method by resistance heating,thereby forming an electron-transporting layer.

Further, lithium fluoride was formed in 1 nm thick over theelectron-transporting layer by an evaporation method by resistanceheating, thereby forming an electron-injecting layer.

Finally, aluminum was formed in 200 nm thick over the electron-injectinglayer by an evaporation method using resistance heating, thereby forminga second electrode. Thus, a comparative light-emitting element 4 wasmanufactured.

Current-voltage characteristics of the light-emitting element 4manufactured in Embodiment 6 and the comparative light-emitting element4 manufactured in Comparative Example 5 are shown in FIG. 15. Moreover,luminance-voltage characteristics thereof are shown in FIG. 16. Further,current efficiency-luminance characteristics thereof are shown in FIG.17.

In the light-emitting element 4, the voltage required to obtain aluminance of 1105 cd/m² was 5.6 V, at which current flowed for 0.31 mA(with a current density of 7.86 mA/cm²). Moreover, the currentefficiency at this time was 14.1 cd/A. Meanwhile, in the comparativelight-emitting element 4, the voltage required to obtain a luminance of1010 cd/m² was 5.8 V, at which current flowed for 0.31 mA (with acurrent density of 7.87 mA/cm²). The current efficiency at this time was12.8 cd/A.

The light-emitting element 4 and the comparative light-emitting element4 have almost the same current-voltage characteristics. However, sincethe current efficiency-luminance characteristics of the light-emittingelement 4 have improved, it is understood that the luminance-voltagecharacteristics have also improved. In other words, it is understoodthat the voltage required to obtain a certain luminance has decreased.

From the above results, it has been confirmed that luminous efficiencyis improved by applying the present invention.

Embodiment 7

This embodiment will describe a light-emitting element of the presentinvention more specifically.

First, indium tin oxide containing silicon oxide was formed over a glasssubstrate by a sputtering method, thereby forming a first electrode. Thefilm thickness thereof was set to 110 nm with an electrode area of 2mm×2 mm.

Next, the substrate where the first electrode was formed was fixed at asubstrate holder provided in a vacuum evaporation apparatus so that asurface of the substrate at which the first electrode was formed facesdownward. After that, the vacuum apparatus was evacuated to reducepressure to be about 10⁻⁴ Pa, and then t-BuDNA and molybdenum oxide (VI)were co-evaporated over the first electrode, thereby forming a layercontaining a composite material. The film thickness was set to 50 nm,and the weight ratio between t-BuDNA and molybdenum oxide (VI) wasadjusted to be 4:1 (=t-BuDNA:molybdenum oxide). A co-evaporation methodis an evaporation method by which evaporation is carried out from aplurality of evaporation sources at the same time within one processchamber.

Next, t-BuDNA was formed in 10 nm thick by an evaporation method usingresistance heating so as to be in contact with the layer containing thecomposite material. The ionization potential of t-BuDNA was 5.55 eV.

By co-evaporating Alq and coumarin 6 further, a 40-nm-thicklight-emitting layer was formed over t-BuDNA. Here, the weight ratiobetween Alq and coumarin 6 was adjusted so as to be 4:0.04(=Alq:coumarin 6). Thus, coumarin 6 exists in such a state that coumarin6 disperses in a layer including Alq.

After that, Alq was formed in 30 nm thick over the light-emitting layerby an evaporation method by resistance heating, thereby forming anelectron-transporting layer.

Further, lithium fluoride was formed in 1 nm thick over theelectron-transporting layer by an evaporation method by resistanceheating, thereby forming an electron-injecting layer.

Finally, aluminum was formed in 200 nm thick over the electron-injectinglayer by an evaporation method by resistance heating, thereby forming asecond electrode. Thus, a light-emitting element 5 was manufactured.

Embodiment 8

This embodiment will describe a light-emitting element of the presentinvention more specifically.

First, indium tin oxide containing silicon oxide was formed over a glasssubstrate by a sputtering method, thereby forming a first electrode. Thefilm thickness thereof was set to 110 nm with an electrode area of 2mm×2 mm.

Next, the substrate where the first electrode was formed was fixed at asubstrate holder provided in a vacuum evaporation apparatus so that asurface of the substrate at which the first electrode was formed facesdownward. After that, the vacuum apparatus was evacuated to reducepressure to be about 10⁻⁴ Pa, and then t-BuDNA and molybdenum oxide (VI)were co-evaporated over the first electrode, thereby forming a layercontaining a composite material. The film thickness was set to 50 nm,and the weight ratio between t-BuDNA and molybdenum oxide (VI) wasadjusted to be 4:1 (=t-BuDNA:molybdenum oxide). A co-evaporation methodis an evaporation method by which evaporation is carried out from aplurality of evaporation sources at the same time within one processchamber. The ionization potential of t-BuDNA was 5.55 eV.

Next, DPPA was formed in 10 nm thick by an evaporation method usingresistance heating so as to be in contact with the layer containing thecomposite material. The ionization potential of DPPA was 5.83 eV.

By co-evaporating Alq and coumarin 6, a 40-nm-thick light-emitting layerwas formed over DPPA. Here, the weight ratio between Alq and coumarin 6was adjusted so as to be 4:0.04 (=Alq:coumarin 6). Thus, coumarin 6exists in such a state that coumarin 6 disperses in a layer includingAlq.

After that, Alq was formed to have a thickness of 30 nm over thelight-emitting layer by an evaporation method by resistance heating,thereby forming an electron-transporting layer.

Further, lithium fluoride was formed in 1 nm thick over theelectron-transporting layer by an evaporation method by resistanceheating, thereby forming an electron-injecting layer.

Finally, aluminum was formed in 200 nm thick over the electron-injectinglayer by an evaporation method by resistance heating, thereby forming asecond electrode. Thus, a light-emitting element 6 was manufactured.

Comparative Example 6

First, indium tin oxide containing silicon oxide was formed over a glasssubstrate by a sputtering method, thereby forming a first electrode. Thefilm thickness thereof was set to 110 nm with an electrode area of 2mm×2 mm.

Next, the substrate where the first electrode was formed was fixed at asubstrate holder provided in a vacuum evaporation apparatus so that asurface of the substrate at which the first electrode was formed facesdownward. After that, the vacuum apparatus was evacuated to reducepressure to be about 10⁻⁴ Pa, and then t-BuDNA and molybdenum oxide (VI)were co-evaporated over the first electrode, thereby forming a layercontaining a composite material. The film thickness was set to 50 nm,and the weight ratio between t-BuDNA and molybdenum oxide (VI) wasadjusted to be 4:1 (=t-BuDNA:molybdenum oxide). A co-evaporation methodis an evaporation method by which evaporation is carried out from aplurality of evaporation sources at the same time within one processchamber.

Next, NPB was formed in 10 nm thick by an evaporation method usingresistance heating.

By co-evaporating Alq and coumarin 6 further, a 40-nm-thicklight-emitting layer was formed over NPB. Here, the weight ratio betweenAlq and coumarin 6 was adjusted so as to be 4:0.04 (=Alq:coumarin 6).Thus, coumarin 6 exists in such a state that coumarin 6 disperses in alayer including Alq.

After that, Alq was formed to have a thickness of 30 nm over thelight-emitting layer by an evaporation method by resistance heating,thereby forming an electron-transporting layer.

Further, lithium fluoride was formed in 1 nm thick over theelectron-transporting layer by an evaporation method by resistanceheating, thereby forming an electron-injecting layer.

Finally, aluminum was formed in 200 nm thick over the electron-injectinglayer by an evaporation method by resistance heating, thereby forming asecond electrode. Thus, a comparative light-emitting element 5 wasmanufactured.

Comparative Example 7

First, indium tin oxide containing silicon oxide was formed over a glasssubstrate by a sputtering method, thereby forming a first electrode. Thefilm thickness thereof was set to 110 nm with an electrode area of 2mm×2 mm.

Next, the substrate where the first electrode was formed was fixed at asubstrate holder provided in a vacuum evaporation apparatus so that asurface of the substrate at which the first electrode was formed facesdownward. After that, the vacuum apparatus was evacuated to reducepressure to be about 10⁻⁴ Pa, and then t-BuDNA and molybdenum oxide (VI)were co-evaporated over the first electrode, thereby forming a layercontaining a composite material. The film thickness was set to 50 nm,and the weight ratio between t-BuDNA and molybdenum oxide (VI) wasadjusted to be 4:1 (=t-BuDNA:molybdenum oxide). A co-evaporation methodis an evaporation method by which evaporation is carried out from aplurality of evaporation sources at the same time within one processchamber.

Next, 4,4′-bis[N-phenyl-N-(spirofluorene-2-yl)]biphenyl (abbreviation:BSPB) was formed in 10 nm thick by an evaporation method usingresistance heating.

By co-evaporating Alq and coumarin 6, a 40-nm-thick light-emitting layerwas formed over BSPB. Here, the weight ratio between Alq and coumarin 6was adjusted so as to be 4:0.04 (=Alq:coumarin 6). Thus, coumarin 6exists in such a state that coumarin 6 disperses in a layer includingAlq.

After that, Alq was formed in 30 nm thick over the light-emitting layerby an evaporation method by resistance heating, thereby forming anelectron-transporting layer.

Further, lithium fluoride was formed in 1 nm thick over theelectron-transporting layer by an evaporation method by resistanceheating, thereby forming an electron-injecting layer.

Finally, aluminum was formed in 200 nm thick over the electron-injectinglayer by an evaporation method by resistance heating, thereby forming asecond electrode. Thus, a comparative light-emitting element 6 wasmanufactured.

Current-voltage characteristics of the light-emitting element 5manufactured in Embodiment 7, the light-emitting element 6 manufacturedin Embodiment 8, the comparative light-emitting element 5 manufacturedin Comparative Example 6, and the comparative light-emitting element 6manufactured in Comparative Example 7 are shown in FIG. 18. Moreover,luminance-voltage characteristics thereof are shown in FIG. 19. Further,current efficiency-luminance characteristics thereof are shown in FIG.20.

In the light-emitting element 5, the voltage required to obtain aluminance of 1202 cd/m² was 5.8 V, at which current flowed for 0.36 mA(with a current density of 9.00 mA/cm²). Moreover, the currentefficiency at this time was 13.4 cd/A Meanwhile, in the light-emittingelement 6, the voltage required to obtain a luminance of 1057 cd/m² was6.0 V, at which current flowed for 0.35 mA (with a current density of8.72 mA/cm²). The current efficiency at this time was 12.1 cd/A. On theother hand, in the comparative light-emitting element 5, the voltagerequired to obtain a luminance of 1103 cd/m² was 6.0 V, at which currentflowed for 0.46 mA (with a current density of 11.54 mA/cm²). Moreover,the current efficiency at this time was 9.6 cd/A. Meanwhile, in thecomparative light-emitting element 6, the voltage required to obtain aluminance of 1159 cd/m² was 5.8 V, at which current flowed for 0.473 mA(with a current density of 11.74 mA/cm²). The current efficiency at thistime was 9.9 cd/A.

The light-emitting elements 5 and 6 have almost the same current-voltagecharacteristics as the comparative light-emitting elements 5 and 6.However, since the current efficiency-luminance characteristics of thelight-emitting elements 5 and 6 have improved as compared with thecomparative light-emitting elements 5 and 6, it is understood that theluminance-voltage characteristics have also improved. In other words, itis understood that the voltage required to obtain a certain luminancehas decreased.

From the above results, it has been confirmed that luminous efficiencyis improved by applying the present invention.

Embodiment 9

This embodiment will describe a light-emitting element of the presentinvention more specifically.

First, indium tin oxide containing silicon oxide was formed over a glasssubstrate by a sputtering method, thereby forming a first electrode. Thefilm thickness thereof was set to 110 nm with an electrode area of 2mm×2 mm.

Next, the substrate where the first electrode was formed was fixed at asubstrate holder provided in a vacuum evaporation apparatus so that asurface of the substrate at which the first electrode was formed facesdownward. After that, the vacuum apparatus was evacuated to reducepressure to be about 10⁻⁴ Pa, and then DNTPD and molybdenum oxide (VI)were co-evaporated over the first electrode, thereby forming a layercontaining a composite material. The film thickness was set to 120 nm,and the weight ratio between DNTPD and molybdenum oxide (VI) wasadjusted to be 1:0.67 (=DNTPD:molybdenum oxide). A co-evaporation methodis an evaporation method by which evaporation is carried out from aplurality of evaporation sources at the same time within one processchamber.

Next, DNTPD was formed in 5 nm thick by an evaporation method usingresistance heating so as to be in contact with the layer containing thecomposite material.

Further, NPB was formed in 5 nm thick over DNTPD by an evaporationmethod using resistance heating.

Subsequently, by co-evaporating Alq and coumarin 6, a 40-nm-thicklight-emitting layer was formed over NPB. Here, the weight ratio betweenAlq and coumarin 6 was adjusted so as to be 1:0.005 (=Alq:coumarin 6).Thus, coumarin 6 exists in such a state that coumarin 6 disperses in alayer including Alq.

After that, Alq was formed in 30 nm thick over the light-emitting layerby an evaporation method by resistance heating, thereby forming anelectron-transporting layer.

Further, lithium fluoride was formed in 1 nm thick over theelectron-transporting layer by an evaporation method by resistanceheating, thereby forming an electron-injecting layer.

Finally, aluminum was formed in 200 nm thick over the electron-injectinglayer by an evaporation method by resistance heating, thereby forming asecond electrode. Thus, a light-emitting element 7 was manufactured.

Comparative Example 8

First, indium tin oxide containing silicon oxide was formed over a glasssubstrate by a sputtering method, thereby forming a first electrode. Thefilm thickness thereof was set to 110 nm with an electrode area of 2mm×2 mm.

Next, the substrate where the first electrode was formed was fixed at asubstrate holder provided in a vacuum evaporation apparatus so that asurface of the substrate at which the first electrode was formed facesdownward. After that, the vacuum apparatus was evacuated to reducepressure to be about 10⁻⁴ Pa, and then DNTPD and molybdenum oxide (VI)were co-evaporated over the first electrode, thereby forming a layercontaining a composite material. The film thickness was set to 120 nm,and the weight ratio between DNTPD and molybdenum oxide (VI) wasadjusted to be 1:0.67 (=DNTPD:molybdenum oxide). A co-evaporation methodis an evaporation method by which evaporation is carried out from aplurality of evaporation sources at the same time within one processchamber.

Next, NPB was formed in 10 nm thick by an evaporation method usingresistance heating.

By co-evaporating Alq and coumarin 6, a 40-nm-thick light-emitting layerwas formed over NPB. Here, the weight ratio between Alq and coumarin 6was adjusted so as to be 1:0.005 (=Alq:coumarin 6). Thus, coumarin 6exists in such a state that coumarin 6 disperses in a layer includingAlq.

After that, Alq was formed in 30 nm thick over the light-emitting layerby an evaporation method by resistance heating, thereby forming anelectron-transporting layer.

Further, lithium fluoride was formed in 1 nm thick over theelectron-transporting layer by an evaporation method using resistanceheating, thereby forming an electron-injecting layer.

Finally, aluminum was formed in 200 nm thick over the electron-injectinglayer by an evaporation method by resistance heating, thereby forming asecond electrode. Thus, a comparative light-emitting element 7 wasmanufactured.

Current-voltage characteristics of the light-emitting element 7manufactured in Embodiment 9 and the comparative light-emitting element7 manufactured in Comparative Example 8 are shown in FIG. 21. Moreover,luminance-voltage characteristics thereof are shown in FIG. 22. Further,current efficiency-luminance characteristics thereof are shown in FIG.23.

In the light-emitting element 7, the voltage required to obtain aluminance of 1287 cd/m² was 5.6 V, at which current flowed for 0.46 mA(with a current density of 11.59 mA/cm²). Moreover, the currentefficiency at this time was 11.1 cd/A. Meanwhile, in the comparativelight-emitting element 7, the voltage required to obtain a luminance of1094 cd/m² was 5.8 V, at which current flowed for 0.47 mA (with acurrent density of 11.74 mA/cm²). Moreover, the current efficiency atthis time was 9.3 cd/A.

The light-emitting element 7 has almost the same current-voltagecharacteristics as the comparative light-emitting element 7. However,since the current efficiency-luminance characteristics of thelight-emitting element 7 have improved, it is understood that theluminance-voltage characteristics have also improved. In other words, itis understood that the voltage required to obtain a certain luminancehas decreased.

From the above results, it has been confirmed that luminous efficiencyis improved by applying the present invention.

Embodiment 10

This embodiment will describe a light-emitting element of the presentinvention more specifically.

First, indium tin oxide containing silicon oxide was formed over a glasssubstrate by a sputtering method, thereby forming a first electrode. Thefilm thickness thereof was set to 110 nm with an electrode area of 2mm×2 mm.

Next, the substrate where the first electrode was formed was fixed at asubstrate holder provided in a vacuum evaporation apparatus so that asurface of the substrate at which the first electrode was formed facesdownward. After that, the vacuum apparatus was evacuated to reducepressure to be about 10⁻⁴ Pa, and then t-BuDNA and molybdenum oxide (VI)were co-evaporated over the first electrode, thereby forming a layercontaining a composite material. The film thickness was set to 20 nm,and the volume ratio between t-BuDNA and molybdenum oxide (VI) wasadjusted so that molybdenum oxide is contained by 10 vol %. Aco-evaporation method is an evaporation method by which evaporation iscarried out from a plurality of evaporation sources at the same timewithin one process chamber.

Next, t-BuDNA was formed in 10 nm thick by an evaporation method usingresistance heating so as to be in contact with the layer containing thecomposite material.

Subsequently, by co-evaporating Alq and DPQd, a 40-nm-thicklight-emitting layer was formed over t-BuDNA. Here, the weight ratiobetween Alq and DPQd was adjusted so as to be 1:0.005 (=Alq:DPQd). Thus,DPQd exists in such a state that DPQd disperses in a layer includingAlq.

After that, Alq was formed to have a thickness of 30 nm over thelight-emitting layer by an evaporation method by resistance heating,thereby forming an electron-transporting layer.

Further, lithium fluoride was formed in 1 nm thick over theelectron-transporting layer by an evaporation method by resistanceheating, thereby forming an electron-injecting layer.

Finally, aluminum was formed in 200 nm thick over the electron-injectinglayer by an evaporation method by resistance heating, thereby forming asecond electrode. Thus, a light-emitting element 8 was manufactured.

Comparative Example 9

First, indium tin oxide containing silicon oxide was formed over a glasssubstrate by a sputtering method, thereby forming a first electrode. Thefilm thickness thereof was set to 110 nm with an electrode area of 2mm×2 mm.

Next, the substrate where the first electrode was formed was fixed at asubstrate holder provided in a vacuum evaporation apparatus so that asurface of the substrate at which the first electrode was formed facesdownward. After that, the vacuum apparatus was evacuated to reducepressure to be about 10⁻⁴ Pa, and then NPB and molybdenum oxide (VI)were co-evaporated over the first electrode, thereby forming a layercontaining a composite material. The film thickness was set to 20 nm,and the volume ratio between NPB and molybdenum oxide (VI) was adjustedso that molybdenum oxide is contained by 10 vol %. A co-evaporationmethod is an evaporation method by which evaporation is carried out froma plurality of evaporation sources at the same time within one processchamber.

Next, t-BuDNA was formed in 10 nm thick by an evaporation method usingresistance heating.

By co-evaporating Alq and DPQd, a 40-nm-thick light-emitting layer wasformed over t-BuDNA. Here, the weight ratio between Alq and DPQd wasadjusted so as to be 1:0.005 (=Alq:DPQd). Thus, DPQd exists in such astate that DPQd disperses in a layer including Alq.

After that, Alq was formed to have a thickness of 30 nm over thelight-emitting layer by an evaporation method by resistance heating,thereby forming an electron-transporting layer.

Further, lithium fluoride was formed in 1 nm thick over theelectron-transporting layer by an evaporation method by resistanceheating, thereby forming an electron-injecting layer.

Finally, aluminum was formed in 200 nm thick over the electron-injectinglayer by an evaporation method by resistance heating, thereby forming asecond electrode. Thus, a comparative light-emitting element 8 wasmanufactured.

Current-voltage characteristics of the light-emitting element 8manufactured in Embodiment 10 and the comparative light-emitting element8 manufactured in Comparative Example 9 are shown in FIG. 24. Moreover,luminance-voltage characteristics thereof are shown in FIG. 25. Further,current efficiency-luminance characteristics thereof are shown in FIG.26.

In the light-emitting element 8, the voltage required to obtain aluminance of 1130 cd/m² was 5.4 V, at which current flowed for 0.27 mA(with a current density of 6.76 mA/cm²). Moreover, the currentefficiency at this time was 16.7 cd/A. Meanwhile, in the comparativelight-emitting element 8, the voltage required to obtain a luminance of1180 cd/m² was 7.4 V, at which current flowed for 0.37 mA (with acurrent density of 9.16 mA/cm²). Moreover, the current efficiency atthis time was 12.9 cd/A.

It is understood that the current-voltage characteristics of thelight-emitting element 8 has improved as compared with the comparativelight-emitting element 8, i.e., current easily flows. Moreover, thecurrent efficiency-luminance characteristics of the light-emittingelement 8 have improved as compared with the comparative light-emittingelement 8, and it is understood that the luminance-voltagecharacteristics have also improved. In other words, it is understoodthat the voltage required to obtain a certain luminance has decreased.

The comparative light-emitting element 8 uses NPB as the organiccompound contained in the layer containing the composite material, anduses t-BuDNA, which is aromatic hydrocarbon having high ionizationpotential, for the layer containing the organic compound provided so asto be in contact with the layer containing the composite material. Inthe comparative light-emitting element 8, since a carrier injectionbarrier between the layer containing the composite material and thelayer containing the organic compound provided so as to be in contactwith the layer containing the composite material is high, drive voltageis high. Moreover, since the layer containing the composite material inthe comparative light-emitting element 8 has an absorption peak in awavelength region of 450 to 800 nm, light emitted from a light-emittingregion is partially absorbed in the layer containing the compositematerial.

Meanwhile, the light-emitting element 8 uses t-BuDNA, which is aromatichydrocarbon having high ionization potential, as the first organiccompound contained in the composite material. Therefore, it becomespossible to use t-BuDNA, which is aromatic hydrocarbon having highionization potential, for the layer containing the second organiccompound provided so as to be in contact with the layer containing thecomposite material. Moreover, since the layer containing the compositematerial uses the same organic compound as the layer provided so as tobe in contact with the layer containing the composite material, thecarrier injection barrier is low. Thus, the drive voltage of thelight-emitting element can be decreased. Moreover, since the layercontaining the composite material in the light-emitting element 8 doesnot have an absorption peak in a wavelength region of 450 to 800 nm,light emitted from the light-emitting region can be extracted to theoutside effectively. Thus, luminous efficiency can be improved.

From the above results, it has been confirmed that the drive voltage ofthe light-emitting element can be decreased and luminous efficiency canbe improved by applying the present invention.

Embodiment 11

This embodiment mode will describe a light-emitting element of thepresent invention more specifically.

First, indium tin oxide containing silicon oxide was formed over a glasssubstrate by a sputtering method, thereby forming a first electrode. Thefilm thickness thereof was set to 110 nm with an electrode area of 2mm×2 mm.

Next, the substrate where the first electrode was formed was fixed at asubstrate holder provided in a vacuum evaporation apparatus so that asurface of the substrate at which the first electrode was formed facesdownward. After that, the vacuum apparatus was evacuated to reducepressure to be about 10⁻⁴ Pa, and then t-BuDNA and molybdenum oxide (VI)were co-evaporated over the first electrode, thereby forming a layercontaining a composite material. The film thickness was set to 50 nm,and the volume ratio between t-BuDNA and molybdenum oxide (VI) wasadjusted so that molybdenum oxide is contained by 10 vol %. Aco-evaporation method is an evaporation method by which evaporation iscarried out from a plurality of evaporation sources at the same timewithin one process chamber.

Next, t-BuDNA was formed in 10 nm thick by an evaporation method usingresistance heating so as to be in contact with the layer containing thecomposite material.

Subsequently, by co-evaporating Alq and DPQd, a 40-nm-thicklight-emitting layer was formed over t-BuDNA. Here, the weight ratiobetween Alq and DPQd was adjusted so as to be 1:0.005 (=Alq:DPQd). Thus,DPQd exists in such a state that DPQd disperses in a layer includingAlq.

After that, Alq was formed to have a thickness of 30 nm over thelight-emitting layer by an evaporation method by resistance heating,thereby forming an electron-transporting layer.

Further, lithium fluoride was formed in 1 nm thick over theelectron-transporting layer by an evaporation method by resistanceheating, thereby forming an electron-injecting layer.

Finally, aluminum was formed in 200 nm thick over the electron-injectinglayer by an evaporation method by resistance heating, thereby forming asecond electrode. Thus, a light-emitting element 9 was manufactured.

Comparative Example 10

First, indium tin oxide containing silicon oxide was formed over a glasssubstrate by a sputtering method, thereby forming a first electrode. Thefilm thickness thereof was set to 110 nm with an electrode area of 2mm×2 mm.

Next, the substrate where the first electrode was formed was fixed at asubstrate holder provided in a vacuum evaporation apparatus so that asurface of the substrate at which the first electrode was formed facesdownward. After that, the vacuum apparatus was evacuated to reducepressure to be about 10⁻⁴ Pa, and then NPB and molybdenum oxide (VI)were co-evaporated over the first electrode, thereby forming a layercontaining a composite material. The film thickness was set to 50 nm,and the volume ratio between NPB and molybdenum oxide (VI) was adjustedso that molybdenum oxide is contained by 10 vol %. A co-evaporationmethod is an evaporation method by which evaporation is carried out froma plurality of evaporation sources at the same time within one processchamber.

Next, t-BuDNA was formed in 10 nm thick by an evaporation method usingresistance heating.

By co-evaporating Alq and DPQd, a 40-nm-thick light-emitting layer wasformed over t-BuDNA. Here, the weight ratio between Alq and DPQd wasadjusted so as to be 1:0.005 (=Alq:DPQd). Thus, DPQd exists in such astate that DPQd disperses in a layer including Alq.

After that, Alq was formed in 30 nm thick over the light-emitting layerby an evaporation method by resistance heating, thereby forming anelectron-transporting layer.

Further, lithium fluoride was formed in 1 nm thick over theelectron-transporting layer by an evaporation method by resistanceheating, thereby forming an electron-injecting layer.

Finally, aluminum was formed in 200 nm thick over the electron-injectinglayer by an evaporation method by resistance heating, thereby forming asecond electrode. Thus, a comparative light-emitting element 9 wasmanufactured.

Current-voltage characteristics of the light-emitting element 9manufactured in Embodiment 11 and the comparative light-emitting element9 manufactured in Comparative Example 10 are shown in FIG. 27. Moreover,luminance-voltage characteristics thereof are shown in FIG. 28. Further,current efficiency-luminance characteristics thereof are shown in FIG.29.

In the light-emitting element 9, the voltage required to obtain aluminance of 1009 cd/m² was 5.6 V, at which current flowed for 0.30 mA(with a current density of 7.46 mA/cm²). Moreover, the currentefficiency at this time was 13.5 cd/A. Meanwhile, in the comparativelight-emitting element 9, the voltage required to obtain a luminance of1295 cd/m² was 7.8 V, at which current flowed for 0.50 mA (with acurrent density of 12.62 mA/cm²). Moreover, the current efficiency atthis time was 10.3 cd/A.

It is understood that the current-voltage characteristics of thelight-emitting element 9 has improved as compared with the comparativelight-emitting element 9, i.e., current easily flows. Moreover, thecurrent efficiency-luminance characteristics of the light-emittingelement 9 have improved as compared with the comparative light-emittingelement 9, and it is understood that the luminance-voltagecharacteristics have also improved. In other words, it is understoodthat the voltage required to obtain a certain luminance has decreased.

The comparative light-emitting element 9 uses NPB as the organiccompound contained in the layer containing the composite material, anduses t-BuDNA, which is aromatic hydrocarbon having high ionizationpotential, for the layer containing the organic compound provided so asto be in contact with the layer containing the composite material. Inthe comparative light-emitting element 9, since a carrier injectionbarrier between the layer containing the composite material and thelayer containing the organic compound provided so as to be in contactwith the layer containing the composite material is high, drive voltageis high. Moreover, since the layer containing the composite material inthe comparative light-emitting element 9 has an absorption peak in awavelength region of 450 to 800 nm, light emitted from a light-emittingregion is partially absorbed in the layer containing the compositematerial.

Meanwhile, the light-emitting element 9 uses t-BuDNA, which is aromatichydrocarbon having high ionization potential, as the first organiccompound contained in the composite material. Therefore, it becomespossible to use t-BuDNA, which is aromatic hydrocarbon having highionization potential, for the layer containing the second organiccompound provided so as to be in contact with the layer containing thecomposite material. Moreover, since the layer containing the compositematerial uses the same organic compound as the layer provided so as tobe in contact with the layer containing the composite material, thecarrier injection barrier is low. Thus, the drive voltage of thelight-emitting element can be decreased. Moreover, since the layercontaining the composite material in the light-emitting element 9 doesnot have an absorption peak in a wavelength region of 450 to 800 nm,light emitted from the light-emitting region can be extracted to theoutside effectively. Thus, luminous efficiency can be improved.

From the above results, it has been confirmed that the drive voltage ofthe light-emitting element can be decreased and luminous efficiency canbe improved by applying the present invention.

Embodiment 12

This embodiment will describe a light-emitting element of the presentinvention more specifically.

First, indium tin oxide containing silicon oxide was formed over a glasssubstrate by a sputtering method, thereby forming a first electrode. Thefilm thickness thereof was set to 110 nm with an electrode area of 2mm×2 mm.

Next, the substrate where the first electrode was formed was fixed at asubstrate holder provided in a vacuum evaporation apparatus so that asurface of the substrate at which the first electrode was formed facesdownward. After that, the vacuum apparatus was evacuated to reducepressure to be about 10⁻⁴ Pa, and then t-BuDNA and molybdenum oxide (VI)were co-evaporated over the first electrode, thereby forming a layercontaining a composite material. The film thickness was set to 150 nm,and the volume ratio between t-BuDNA and molybdenum oxide (VI) wasadjusted so that molybdenum oxide is contained by 10 vol %. Aco-evaporation method is an evaporation method by which evaporation iscarried out from a plurality of evaporation sources at the same timewithin one process chamber.

Next, t-BuDNA was formed in 10 nm thick by an evaporation method usingresistance heating so as to be in contact with the layer containing acomposite material.

Subsequently, by co-evaporating Alq and DPQd, a 40-nm-thicklight-emitting layer was formed over t-BuDNA. Here, the weight ratiobetween Alq and DPQd was adjusted so as to be 1:0.005 (=Alq:DPQd). Thus,DPQd exists in such a state that DPQd disperses in a layer includingAlq.

After that, Alq was formed to have a thickness of 30 nm over thelight-emitting layer by an evaporation method by resistance heating,thereby forming an electron-transporting layer.

Further, lithium fluoride was formed in 1 nm thick over theelectron-transporting layer by an evaporation method by resistanceheating, thereby forming an electron-injecting layer.

Finally, aluminum was formed in 200 nm thick over the electron-injectinglayer by an evaporation method by resistance heating, thereby forming asecond electrode. Thus, a light-emitting element 10 was manufactured.

Comparative Example 11

First, indium tin oxide containing silicon oxide was formed over a glasssubstrate by a sputtering method, thereby forming a first electrode. Thefilm thickness thereof was set to 110 nm with an electrode area of 2mm×2 mm.

Next, the substrate where the first electrode was formed was fixed at asubstrate holder provided in a vacuum evaporation apparatus so that asurface of the substrate at which the first electrode was formed facesdownward. After that, the vacuum apparatus was evacuated to reducepressure to be about 10⁻⁴ Pa, and then NPB and molybdenum oxide (VI)were co-evaporated over the first electrode, thereby forming a layercontaining a composite material. The film thickness was set to 150 nm,and the volume ratio between NPB and molybdenum oxide (VI) was adjustedso that molybdenum oxide is contained by 10 vol %. A co-evaporationmethod is an evaporation method by which evaporation is carried out froma plurality of evaporation sources at the same time within one processchamber.

Next, t-BuDNA was formed in 10 nm thick by an evaporation method usingresistance heating.

By co-evaporating Alq and DPQd, a 40-nm-thick light-emitting layer wasformed over t-BuDNA. Here, the weight ratio between Alq and DPQd wasadjusted so as to be 1:0.005 (=Alq:DPQd). Thus, DPQd exists in such astate that DPQd disperses in a layer including Alq.

After that, Alq was formed in 30 nm thick over the light-emitting layerby an evaporation method by resistance heating, thereby forming anelectron-transporting layer.

Further, lithium fluoride was formed in 1 nm thick over theelectron-transporting layer by an evaporation method using resistanceheating, thereby forming an electron-injecting layer.

Finally, aluminum was formed in 200 nm thick over the electron-injectinglayer by an evaporation method by resistance heating, thereby forming asecond electrode. Thus, a comparative light-emitting element 10 wasmanufactured.

Current-voltage characteristics of the light-emitting element 10manufactured in Embodiment 12 and the comparative light-emitting element10 manufactured in Comparative Example 11 are shown in FIG. 30.Moreover, luminance-voltage characteristics thereof are shown in FIG.31. Further, current efficiency-luminance characteristics thereof areshown in FIG. 32.

In the light-emitting element 10, the voltage required to obtain aluminance of 1087 cd/m² was 5.4 V, at which current flowed for 0.30 mA(with a current density of 7.51 mA/cm²). Moreover, the currentefficiency at this time was 14.5 cd/A. Meanwhile, in the comparativelight-emitting element 10, the voltage required to obtain a luminance of1272 cd/m² was 7.6 V, at which current flowed for 0.45 mA (with acurrent density of 11.17 mA/cm²). Moreover, the current efficiency atthis time was 11.4 cd/A.

It is understood that the current-voltage characteristics of thelight-emitting element 10 has improved as compared with the comparativelight-emitting element 10, i.e., current easily flows. Moreover, thecurrent efficiency-luminance characteristics of the light-emittingelement 10 have improved as compared with the comparative light-emittingelement 10, and it is understood that the luminance-voltagecharacteristics have also improved. In other words, it is understoodthat the voltage required to obtain a certain luminance has decreased.

The comparative light-emitting element 10 uses NPB as the organiccompound contained in the layer containing the composite material, anduses t-BuDNA, which is aromatic hydrocarbon having high ionizationpotential, for the layer containing the organic compound provided so asto be in contact with the layer containing the composite material. Inthe comparative light-emitting element 10, since a carrier injectionbarrier between the layer containing the composite material and thelayer containing the organic compound provided so as to be in contactwith the layer containing the composite material is high, drive voltageis high. Moreover, since the layer containing the composite material inthe comparative light-emitting element 10 has an absorption peak in awavelength region of 450 to 800 nm, light emitted from a light-emittingregion is partially absorbed in the layer containing the compositematerial.

Meanwhile, the light-emitting element 10 uses t-BuDNA, which is aromatichydrocarbon having high ionization potential, as the first organiccompound contained in the composite material. Therefore, it becomespossible to use t-BuDNA, which is aromatic hydrocarbon having highionization potential, for the layer containing the second organiccompound provided so as to be in contact with the layer containing thecomposite material. Moreover, since the layer containing the compositematerial uses the same organic compound as the layer provided so as tobe in contact with the layer containing the composite material, thecarrier injection barrier is low. Thus, the drive voltage of thelight-emitting element can be decreased. Moreover, since the layercontaining the composite material in the light-emitting element 10 doesnot have an absorption peak in a wavelength region of 450 to 800 nm,light emitted from the light-emitting region can be extracted to theoutside effectively. Thus, luminous efficiency can be improved.

From the above results, it has been confirmed that the drive voltage ofthe light-emitting element can be decreased and luminous efficiency canbe improved by applying the present invention.

Embodiment 13

This embodiment will describe a light-emitting element of the presentinvention more specifically.

First, indium tin oxide containing silicon oxide was formed over a glasssubstrate by a sputtering method, thereby forming a first electrode. Thefilm thickness thereof was set to 110 nm with an electrode area of 2mm×2 mm.

Next, the substrate where the first electrode was formed was fixed at asubstrate holder provided in a vacuum evaporation apparatus so that asurface of the substrate at which the first electrode was formed facesdownward. After that, the vacuum apparatus was evacuated to reducepressure to be about 10⁻⁴ Pa, and then t-BuDNA and molybdenum oxide (VI)were co-evaporated over the first electrode, thereby forming a layercontaining a composite material. The film thickness was set to 50 nm,and the weight ratio between t-BuDNA and molybdenum oxide (VI) wasadjusted to be 4:1 (=t-BuDNA:molybdenum oxide). A co-evaporation methodis an evaporation method by which evaporation is carried out from aplurality of evaporation sources at the same time within one processchamber.

Next, t-BuDNA was formed in 10 nm thick by an evaporation method usingresistance heating so as to be in contact with the layer containing thecomposite material.

Subsequently, by co-evaporating9-[4-(N-carbazolyl)]phenyl-10-phenylanthracene (abbreviation: CzPA) and9-(4-{N-[4-(9-carbazolyl)phenyl]-N-phenylamino}phenyl)-10-phenylanthracene(abbreviation: YGAPA), a 30-nm-thick light-emitting layer was formedover t-BuDNA. Here, the weight ratio between CzPA and YGAPA was adjustedso as to be 4:0.16 (=CzPA:YGAPA).

After that, BPhen was formed in 5 nm thick and Alq was formed in 30 nmthick, over the light-emitting layer by an evaporation method byresistance heating, thereby forming an electron-transporting layer.

Further, lithium fluoride was formed in 1 nm thick over theelectron-transporting layer by an evaporation method using resistanceheating, thereby forming an electron-injecting layer.

Finally, aluminum was formed in 200 nm thick over the electron-injectinglayer by an evaporation method by resistance heating, thereby forming asecond electrode. Thus, a light-emitting element 11 was manufactured.

Current-voltage characteristics of the light-emitting element 11manufactured in Embodiment 13 are shown in FIG. 39. Moreover,luminance-voltage characteristics thereof are shown in FIG. 40. Further,current efficiency-luminance characteristics thereof are shown in FIG.41.

In the light-emitting element 11, the voltage required to obtain aluminance of 1023 cd/m² was 10.6 V, at which current flowed for 2.46 mA(with a current density of 61.5 mA/cm²). Moreover, at this time, thecurrent efficiency was 1.66 cd/A and the CIE chromaticity was (x,y=0.16, 0.13), and blue light emission was obtained.

The light-emitting element 11 uses t-BuDNA, which is aromatichydrocarbon having high ionization potential, as the first organiccompound contained in the composite material. Therefore, it becomespossible to use t-BuDNA, which is aromatic hydrocarbon having highionization potential, for the layer containing the second organiccompound provided so as to be in contact with the layer containing thecomposite material. Moreover, since the layer containing the compositematerial uses the same organic compound as the layer provided so as tobe in contact with the layer containing the composite material, thecarrier injection barrier is low. Thus, the drive voltage of thelight-emitting element can be decreased. Moreover, since the layercontaining the composite material in the light-emitting element 11 doesnot have an absorption peak in a wavelength region of 450 to 800 nm,light emitted from the light-emitting region can be extracted to theoutside effectively. Thus, luminous efficiency can be improved.

From the above results, it has been confirmed that the drive voltage ofthe light-emitting element can be decreased and luminous efficiency canbe improved by applying the present invention.

This application is based on Japanese Patent Application serial no.2005-213759 filed in Japan Patent Office on Jul. 25, 2005 and JapanesePatent Application serial no. 2005-230272 filed in Japan Patent Officeon Aug. 9, 2005, the entire contents of which are hereby incorporated byreference.

1. A light-emitting element comprising: a multilayer body in which afirst layer containing a composite material of a first organic compoundand an inorganic compound and a second layer containing a second organiccompound are stacked, the second layer being in contact with the firstlayer, wherein the multilayer body is provided between a first electrodeand a second electrode, and wherein the multilayer body does not have apeak of an absorption spectrum in a wavelength region of 450 to 800 nm.2. A light-emitting element comprising: a multilayer body in which afirst layer containing a first composite material of a first organiccompound and an inorganic compound and a second layer containing asecond organic compound are stacked, the second layer being in contactwith the first layer, wherein the multilayer body is provided between afirst electrode and a second electrode, wherein the first compositematerial has a transmittance of 80% or higher in a wavelength region of450 to 800 nm, and wherein a second composite material of the secondorganic compound and the inorganic compound has a transmittance of 80%or higher in a wavelength region of 450 to 800 nm.
 3. A light-emittingelement comprising: a multilayer body in which a first layer containinga first composite material of a first organic compound and an inorganiccompound and a second layer containing a second organic compound, whichis provided so as to be in contact with the first layer are stacked,wherein the multilayer body is provided between a first electrode and asecond electrode, wherein the first composite material has an absorbancethat satisfies a formula (1) in a wavelength region of 450 to 800 nm,and wherein a second composite material of the second organic compoundand the inorganic compound has an absorbance that satisfies the formula(1) in a wavelength region of 450 to 800 nm:A≦9.7×10⁻⁴ ×l  (1) A: absorbance l: thickness (nm).
 4. Thelight-emitting element according to claim 1 further comprising: alight-emitting layer containing a light-emitting substance, wherein thelight-emitting layer are provided between the multilayer body and thesecond electrode, wherein the first layer is provided so as to be incontact with the first electrode, and wherein the light-emittingsubstance emits light when voltage is applied so that the firstelectrode has a higher potential than the second electrode.
 5. Thelight-emitting element according to claim 2 further comprising: alight-emitting layer containing a light-emitting substance, wherein thelight-emitting layer are provided between the multilayer body and thesecond electrode, wherein the first layer is provided so as to be incontact with the first electrode, and wherein the light-emittingsubstance emits light when voltage is applied so that the firstelectrode has a higher potential than the second electrode.
 6. The lightemitting element according to claim 2, wherein the first compositematerial has a thickness of 100 nm, and wherein the second compositematerial has a thickness of 100 nm.
 7. The light-emitting elementaccording to claim 3 further comprising: a light-emitting layercontaining a light-emitting substance, wherein the light-emitting layerare provided between the multilayer body and the second electrode,wherein the first layer is provided so as to be in contact with thefirst electrode, and wherein the light-emitting substance emits lightwhen voltage is applied so that the first electrode has a higherpotential than the second electrode.
 8. The light-emitting elementaccording to any one of claims 1 to 3, wherein the first organiccompound is aromatic hydrocarbon.
 9. The light-emitting elementaccording to any one of claims 1 to 3, wherein the first organiccompound is an anthracene derivative.
 10. A light-emitting elementcomprising: a multilayer body in which a first layer containing acomposite material of a first organic compound and an inorganic compoundand a second layer containing a second organic compound, which isprovided so as to be in contact with the first layer are stacked,wherein the multilayer body is provided between a pair of electrodes,and wherein the first organic compound is aromatic hydrocarbon.
 11. Alight-emitting element comprising: a multilayer body in which a firstlayer containing a composite material of a first organic compound and aninorganic compound and a second layer containing a second organiccompound, which is provided so as to be in contact with the first layerare stacked, wherein the multilayer body is provided between a pair ofelectrodes, and wherein the first organic compound is an anthracenederivative.
 12. The light-emitting element according to any one ofclaims 1 to 3, 10 and 11, wherein an ionizing potential Ip (1) of thefirst organic compound and an ionizing potential Ip (2) of the secondorganic compound satisfy:Ip(2)≦Ip(1)+0.5 eV.
 13. The light-emitting element according to any oneof claims 1 to 3, 10 and 11, wherein the second organic compound isaromatic hydrocarbon.
 14. The light-emitting element according to anyone of claims 1 to 3, 10 and 11, wherein the second organic compound isan anthracene derivative.
 15. The light-emitting element according toany one of claims 1 to 3, 10 and 11, wherein the second organic compoundis a carbazole derivative.
 16. The light-emitting element according toany one of claims 1 to 3, 10 and 11, wherein the second layer containingthe second organic compound has a thickness from 1 to 20 nm.
 17. Thelight-emitting element according to any one of claims 1 to 3, 10 and 11,wherein the inorganic compound has an electron-accepting property withrespect to the first organic compound.
 18. The light-emitting elementaccording to any one of claims 1 to 3, 10 and 11, wherein the inorganiccompound is an oxide of a transition metal.
 19. The light-emittingelement according to any one of claims 1 to 3, 10 and 11, wherein theinorganic compound is an oxide of a metal belonging to any of Group 4 toGroup 8 in the periodic table.
 20. The light-emitting element accordingto any one of claims 1 to 3, 10 and 11, wherein the inorganic compoundis any of vanadium oxide, niobium oxide, tantalum oxide, chromium oxide,molybdenum oxide, tungsten oxide, manganese oxide, and rhenium oxide.21. A light-emitting element comprising: a first layer containing acomposite material of an organic compound and an inorganic compound; anda second layer containing the organic compound, which is provided so asto be in contact with the first layer, wherein the first layer and thesecond layer are provided between a first electrode and a secondelectrode, and wherein the composite material does not have a peak of anabsorption spectrum in a wavelength region of 450 to 800 nm.
 22. Alight-emitting element comprising: a first layer containing a compositematerial of an organic compound and an inorganic compound; and a secondlayer containing the organic compound, which is provided so as to be incontact with the first layer, wherein the first layer and the secondlayer are provided between a first electrode and a second electrode, andwherein the composite material has a transmittance of 80% or higher in awavelength region of 450 to 800 nm.
 23. A light-emitting elementcomprising: a first layer containing a composite material of an organiccompound and an inorganic compound; and a second layer containing theorganic compound, which is provided so as to be in contact with thefirst layer, wherein the first layer and the second layer are providedbetween a first electrode and a second electrode, and wherein thecomposite material has an absorbance that satisfies a formula (1) in awavelength region of 450 to 800 nm:A≦9.7×l×10⁻⁴ ×l  (1) A: absorbance l: thickness (nm).
 24. Thelight-emitting element according to claim 21 further comprising: alight-emitting layer containing a light-emitting substance, wherein thelight-emitting layer are provided between the second layer and thesecond electrode, wherein the first layer is provided so as to be incontact with the first electrode, and wherein the light-emittingsubstance emits light when voltage is applied so that the firstelectrode has a higher potential than the second electrode.
 25. Thelight-emitting element according to claim 22 further comprising: alight-emitting layer containing a light-emitting substance, wherein thelight-emitting layer are provided between the second layer and a secondelectrode, wherein the first layer is provided so as to be in contactwith the first electrode, and wherein the light-emitting substance emitslight when voltage is applied so that the first electrode has a higherpotential than the second electrode.
 26. The light emitting elementaccording to claim 22, wherein the composite material has a thickness of100 nm.
 27. The light-emitting element according to claim 23 furthercomprising: a light-emitting layer containing a light-emittingsubstance, wherein the light-emitting layer are provided between thesecond layer and the second electrode, wherein the first layer isprovided so as to be in contact with the first electrode, and whereinthe light-emitting substance emits light when voltage is applied so thatthe first electrode has a higher potential than the second electrode.28. The light-emitting element according to any one of claims 21 to 23,wherein the organic compound is aromatic hydrocarbon.
 29. Thelight-emitting element according to any one of claims 21 to 23, whereinthe organic compound is an anthracene derivative.
 30. A light-emittingelement comprising: a first layer containing a composite material of anorganic compound and an inorganic compound; and a second layercontaining the organic compound, which is provided so as to be incontact with the first layer, wherein the first layer and the secondlayer are provided between a pair of electrodes, and wherein the organiccompound is aromatic hydrocarbon.
 31. A light-emitting elementcomprising: a first layer containing a composite material of an organiccompound and an inorganic compound; and a second layer containing theorganic compound, which is provided so as to be in contact with thefirst layer, wherein the first layer and the second layer are providedbetween a pair of electrodes, and wherein the organic compound is ananthracene derivative.
 32. The light-emitting element according to anyone of claims 21 to 23, 30 and 31, wherein the second layer containingthe organic compound has a thickness from 1 to 20 ran.
 33. Thelight-emitting element according to any one of claims 21 to 23, 30 and31, wherein the inorganic compound has an electron-accepting propertywith respect to the organic compound.
 34. The light-emitting elementaccording to any one of claims 21 to 23, 30 and 31, wherein theinorganic compound is an oxide of a transition metal.
 35. Thelight-emitting element according to any one of claims 21 to 23, 30 and31, wherein the inorganic compound is an oxide of a metal belonging toany of Group 4 to Group 8 in the periodic table.
 36. The light-emittingelement according to any one of claims 21 to 23, 30 and 31, wherein theinorganic compound is any of vanadium oxide, niobium oxide, tantalumoxide, chromium oxide, molybdenum oxide, tungsten oxide, manganeseoxide, and rhenium oxide.
 37. A light-emitting device comprising: thelight-emitting element according to any one of claims 1 to 3, 10, 11, 21to 23, and 31; and controlling means for controlling light emission ofthe light-emitting element.
 38. An electronic appliance comprising: adisplay portion; the light-emitting element according to any one ofclaims 1 to 3, 10, 11, 21 to 23, and 31; and controlling means forcontrolling light emission of the light-emitting element.
 39. Alight-emitting element comprising: a multilayer body in which a firstlayer containing a first composite material of a first organic compoundand an inorganic compound and a second layer containing a second organiccompound are stacked, the second layer being in contact with the firstlayer, wherein the multilayer body is provided between a first electrodeand a second electrode, wherein the multilayer body has a transmittanceof 80% or higher in a wavelength region of 450 to 800 nm.
 40. Alight-emitting element comprising: a first layer containing a compositematerial of an organic compound and an inorganic compound; and a secondlayer containing the organic compound, which is provided so as to be incontact with the first layer, wherein the first layer and the secondlayer are provided between a first electrode and a second electrode; andwherein a multilayer body in which the first layer and the second layerare stacked has a transmittance of 80% or higher in a wavelength regionof 450 to 800 nm.